diff --git a/internal/testserdes/testing.go b/internal/testserdes/testing.go
index 0be71a844..d30e1ddaa 100644
--- a/internal/testserdes/testing.go
+++ b/internal/testserdes/testing.go
@@ -5,6 +5,7 @@ import (
 	"testing"
 
 	"github.com/nspcc-dev/neo-go/pkg/io"
+	"github.com/nspcc-dev/neo-go/pkg/vm/stackitem"
 	"github.com/stretchr/testify/require"
 )
 
@@ -26,6 +27,15 @@ func EncodeDecodeBinary(t *testing.T, expected, actual io.Serializable) {
 	require.Equal(t, expected, actual)
 }
 
+// ToFromStackItem checks if expected stays the same after converting to/from
+// StackItem.
+func ToFromStackItem(t *testing.T, expected, actual stackitem.Convertible) {
+	item, err := expected.ToStackItem()
+	require.NoError(t, err)
+	require.NoError(t, actual.FromStackItem(item))
+	require.Equal(t, expected, actual)
+}
+
 // EncodeBinary serializes a to a byte slice.
 func EncodeBinary(a io.Serializable) ([]byte, error) {
 	w := io.NewBufBinWriter()
diff --git a/pkg/compiler/assign_test.go b/pkg/compiler/assign_test.go
index 4c7007a0f..182224ea4 100644
--- a/pkg/compiler/assign_test.go
+++ b/pkg/compiler/assign_test.go
@@ -3,8 +3,6 @@ package compiler_test
 import (
 	"math/big"
 	"testing"
-
-	"github.com/nspcc-dev/neo-go/pkg/vm/stackitem"
 )
 
 var assignTestCases = []testCase{
@@ -154,9 +152,9 @@ func TestManyAssignments(t *testing.T) {
 	src2 := `return a
 	}`
 
-	for i := 0; i < stackitem.MaxArraySize; i++ {
+	for i := 0; i < 1024; i++ {
 		src1 += "a += 1\n"
 	}
 
-	eval(t, src1+src2, big.NewInt(stackitem.MaxArraySize))
+	eval(t, src1+src2, big.NewInt(1024))
 }
diff --git a/pkg/core/blockchain.go b/pkg/core/blockchain.go
index c62a3e202..5a820a967 100644
--- a/pkg/core/blockchain.go
+++ b/pkg/core/blockchain.go
@@ -361,24 +361,18 @@ func (bc *Blockchain) init() error {
 		if storedCS == nil {
 			return fmt.Errorf("native contract %s is not stored", md.Name)
 		}
-		w := io.NewBufBinWriter()
-		storedCS.EncodeBinary(w.BinWriter)
-		if w.Err != nil {
-			return fmt.Errorf("failed to check native %s state against autogenerated one: %w", md.Name, w.Err)
+		storedCSBytes, err := stackitem.SerializeConvertible(storedCS)
+		if err != nil {
+			return fmt.Errorf("failed to check native %s state against autogenerated one: %w", md.Name, err)
 		}
-		buff := w.Bytes()
-		storedCSBytes := make([]byte, len(buff))
-		copy(storedCSBytes, buff)
-		w.Reset()
 		autogenCS := &state.Contract{
 			ContractBase:  md.ContractBase,
 			UpdateCounter: storedCS.UpdateCounter, // it can be restored only from the DB, so use the stored value.
 		}
-		autogenCS.EncodeBinary(w.BinWriter)
-		if w.Err != nil {
-			return fmt.Errorf("failed to check native %s state against autogenerated one: %w", md.Name, w.Err)
+		autogenCSBytes, err := stackitem.SerializeConvertible(autogenCS)
+		if err != nil {
+			return fmt.Errorf("failed to check native %s state against autogenerated one: %w", md.Name, err)
 		}
-		autogenCSBytes := w.Bytes()
 		if !bytes.Equal(storedCSBytes, autogenCSBytes) {
 			return fmt.Errorf("native %s: version mismatch (stored contract state differs from autogenerated one), "+
 				"try to resynchronize the node from the genesis", md.Name)
diff --git a/pkg/core/fee/opcode.go b/pkg/core/fee/opcode.go
index b9c788dbc..806ee1a8d 100644
--- a/pkg/core/fee/opcode.go
+++ b/pkg/core/fee/opcode.go
@@ -164,7 +164,7 @@ var coefficients = map[opcode.Opcode]int64{
 	opcode.DIV:          1 << 3,
 	opcode.MOD:          1 << 3,
 	opcode.POW:          1 << 6,
-	opcode.SQRT:         1 << 11,
+	opcode.SQRT:         1 << 6,
 	opcode.SHL:          1 << 3,
 	opcode.SHR:          1 << 3,
 	opcode.NOT:          1 << 2,
diff --git a/pkg/core/interop_system.go b/pkg/core/interop_system.go
index e7578180f..e83e3880f 100644
--- a/pkg/core/interop_system.go
+++ b/pkg/core/interop_system.go
@@ -219,8 +219,9 @@ func storageFind(ic *interop.Context) error {
 // given m and a set of public keys.
 func contractCreateMultisigAccount(ic *interop.Context) error {
 	m := ic.VM.Estack().Pop().BigInt()
-	if !m.IsInt64() || m.Int64() > math.MaxInt32 {
-		return errors.New("m should fit int32")
+	mu64 := m.Uint64()
+	if !m.IsUint64() || mu64 > math.MaxInt32 {
+		return errors.New("m must be positive and fit int32")
 	}
 	arr := ic.VM.Estack().Pop().Array()
 	pubs := make(keys.PublicKeys, len(arr))
@@ -231,7 +232,7 @@ func contractCreateMultisigAccount(ic *interop.Context) error {
 		}
 		pubs[i] = p
 	}
-	script, err := smartcontract.CreateMultiSigRedeemScript(int(m.Int64()), pubs)
+	script, err := smartcontract.CreateMultiSigRedeemScript(int(mu64), pubs)
 	if err != nil {
 		return err
 	}
diff --git a/pkg/core/native/designate.go b/pkg/core/native/designate.go
index 05f387dec..8c75eebc8 100644
--- a/pkg/core/native/designate.go
+++ b/pkg/core/native/designate.go
@@ -18,7 +18,6 @@ import (
 	"github.com/nspcc-dev/neo-go/pkg/core/state"
 	"github.com/nspcc-dev/neo-go/pkg/crypto/hash"
 	"github.com/nspcc-dev/neo-go/pkg/crypto/keys"
-	"github.com/nspcc-dev/neo-go/pkg/io"
 	"github.com/nspcc-dev/neo-go/pkg/smartcontract"
 	"github.com/nspcc-dev/neo-go/pkg/smartcontract/callflag"
 	"github.com/nspcc-dev/neo-go/pkg/smartcontract/manifest"
@@ -272,10 +271,9 @@ func (s *Designate) GetDesignatedByRole(d dao.DAO, r noderoles.Role, index uint3
 		}
 	}
 	if resSi != nil {
-		reader := io.NewBinReaderFromBuf(resSi)
-		ns.DecodeBinary(reader)
-		if reader.Err != nil {
-			return nil, 0, reader.Err
+		err = stackitem.DeserializeConvertible(resSi, &ns)
+		if err != nil {
+			return nil, 0, err
 		}
 	}
 	return keys.PublicKeys(ns), bestIndex, err
@@ -287,7 +285,7 @@ func (s *Designate) designateAsRole(ic *interop.Context, args []stackitem.Item)
 		panic(ErrInvalidRole)
 	}
 	var ns NodeList
-	if err := ns.fromStackItem(args[1]); err != nil {
+	if err := ns.FromStackItem(args[1]); err != nil {
 		panic(err)
 	}
 
@@ -326,8 +324,9 @@ func (s *Designate) DesignateAsRole(ic *interop.Context, r noderoles.Role, pubs
 		return ErrAlreadyDesignated
 	}
 	sort.Sort(pubs)
+	nl := NodeList(pubs)
 	s.rolesChangedFlag.Store(true)
-	err := ic.DAO.PutStorageItem(s.ID, key, NodeList(pubs).Bytes())
+	err := putConvertibleToDAO(s.ID, ic.DAO, key, &nl)
 	if err != nil {
 		return err
 	}
diff --git a/pkg/core/native/ledger.go b/pkg/core/native/ledger.go
index 969bf26dc..8c901162c 100644
--- a/pkg/core/native/ledger.go
+++ b/pkg/core/native/ledger.go
@@ -157,9 +157,9 @@ func isTraceableBlock(bc blockchainer.Blockchainer, index uint32) bool {
 // be called within VM context, so it panics if anything goes wrong.
 func getBlockHashFromItem(bc blockchainer.Blockchainer, item stackitem.Item) util.Uint256 {
 	bigindex, err := item.TryInteger()
-	if err == nil && bigindex.IsInt64() {
-		index := bigindex.Int64()
-		if index < 0 || index > math.MaxUint32 {
+	if err == nil && bigindex.IsUint64() {
+		index := bigindex.Uint64()
+		if index > math.MaxUint32 {
 			panic("bad block index")
 		}
 		if uint32(index) > bc.BlockHeight() {
diff --git a/pkg/core/native/management.go b/pkg/core/native/management.go
index 032bf3571..a5eb71c52 100644
--- a/pkg/core/native/management.go
+++ b/pkg/core/native/management.go
@@ -16,7 +16,6 @@ import (
 	"github.com/nspcc-dev/neo-go/pkg/core/state"
 	"github.com/nspcc-dev/neo-go/pkg/core/storage"
 	"github.com/nspcc-dev/neo-go/pkg/encoding/bigint"
-	"github.com/nspcc-dev/neo-go/pkg/io"
 	"github.com/nspcc-dev/neo-go/pkg/smartcontract"
 	"github.com/nspcc-dev/neo-go/pkg/smartcontract/callflag"
 	"github.com/nspcc-dev/neo-go/pkg/smartcontract/manifest"
@@ -155,7 +154,7 @@ func (m *Management) GetContract(d dao.DAO, hash util.Uint160) (*state.Contract,
 func (m *Management) getContractFromDAO(d dao.DAO, hash util.Uint160) (*state.Contract, error) {
 	contract := new(state.Contract)
 	key := makeContractKey(hash)
-	err := getSerializableFromDAO(m.ID, d, key, contract)
+	err := getConvertibleFromDAO(m.ID, d, key, contract)
 	if err != nil {
 		return nil, err
 	}
@@ -487,14 +486,12 @@ func (m *Management) InitializeCache(d dao.DAO) error {
 
 	var initErr error
 	d.Seek(m.ID, []byte{prefixContract}, func(_, v []byte) {
-		var cs state.Contract
-		r := io.NewBinReaderFromBuf(v)
-		cs.DecodeBinary(r)
-		if r.Err != nil {
-			initErr = r.Err
+		var cs = new(state.Contract)
+		initErr = stackitem.DeserializeConvertible(v, cs)
+		if initErr != nil {
 			return
 		}
-		m.contracts[cs.Hash] = &cs
+		m.contracts[cs.Hash] = cs
 	})
 	return initErr
 }
@@ -529,7 +526,7 @@ func (m *Management) Initialize(ic *interop.Context) error {
 // PutContractState saves given contract state into given DAO.
 func (m *Management) PutContractState(d dao.DAO, cs *state.Contract) error {
 	key := makeContractKey(cs.Hash)
-	if err := putSerializableToDAO(m.ID, d, key, cs); err != nil {
+	if err := putConvertibleToDAO(m.ID, d, key, cs); err != nil {
 		return err
 	}
 	m.markUpdated(cs.Hash)
diff --git a/pkg/core/native/native_neo.go b/pkg/core/native/native_neo.go
index dadeaee35..3726d9063 100644
--- a/pkg/core/native/native_neo.go
+++ b/pkg/core/native/native_neo.go
@@ -20,7 +20,6 @@ import (
 	"github.com/nspcc-dev/neo-go/pkg/crypto/hash"
 	"github.com/nspcc-dev/neo-go/pkg/crypto/keys"
 	"github.com/nspcc-dev/neo-go/pkg/encoding/bigint"
-	"github.com/nspcc-dev/neo-go/pkg/io"
 	"github.com/nspcc-dev/neo-go/pkg/smartcontract"
 	"github.com/nspcc-dev/neo-go/pkg/smartcontract/callflag"
 	"github.com/nspcc-dev/neo-go/pkg/smartcontract/manifest"
@@ -698,7 +697,7 @@ func (n *NEO) RegisterCandidateInternal(ic *interop.Context, pub *keys.PublicKey
 		c = new(candidate).FromBytes(si)
 		c.Registered = true
 	}
-	return ic.DAO.PutStorageItem(n.ID, key, c.Bytes())
+	return putConvertibleToDAO(n.ID, ic.DAO, key, c)
 }
 
 func (n *NEO) unregisterCandidate(ic *interop.Context, args []stackitem.Item) stackitem.Item {
@@ -727,7 +726,7 @@ func (n *NEO) UnregisterCandidateInternal(ic *interop.Context, pub *keys.PublicK
 	if ok {
 		return err
 	}
-	return ic.DAO.PutStorageItem(n.ID, key, c.Bytes())
+	return putConvertibleToDAO(n.ID, ic.DAO, key, c)
 }
 
 func (n *NEO) vote(ic *interop.Context, args []stackitem.Item) stackitem.Item {
@@ -820,7 +819,7 @@ func (n *NEO) ModifyAccountVotes(acc *state.NEOBalanceState, d dao.DAO, value *b
 			}
 		}
 		n.validators.Store(keys.PublicKeys(nil))
-		return d.PutStorageItem(n.ID, key, cd.Bytes())
+		return putConvertibleToDAO(n.ID, d, key, cd)
 	}
 	return nil
 }
@@ -903,10 +902,9 @@ func (n *NEO) getAccountState(ic *interop.Context, args []stackitem.Item) stacki
 		return stackitem.Null{}
 	}
 
-	r := io.NewBinReaderFromBuf(si)
-	item := stackitem.DecodeBinary(r)
-	if r.Err != nil {
-		panic(r.Err) // no errors are expected but we better be sure
+	item, err := stackitem.Deserialize(si)
+	if err != nil {
+		panic(err) // no errors are expected but we better be sure
 	}
 	return item
 }
diff --git a/pkg/core/native/native_neo_candidate.go b/pkg/core/native/native_neo_candidate.go
index a1a7bb44f..8a1d6ca84 100644
--- a/pkg/core/native/native_neo_candidate.go
+++ b/pkg/core/native/native_neo_candidate.go
@@ -3,7 +3,6 @@ package native
 import (
 	"math/big"
 
-	"github.com/nspcc-dev/neo-go/pkg/io"
 	"github.com/nspcc-dev/neo-go/pkg/vm/stackitem"
 )
 
@@ -12,40 +11,35 @@ type candidate struct {
 	Votes      big.Int
 }
 
-// Bytes marshals c to byte array.
-func (c *candidate) Bytes() []byte {
-	w := io.NewBufBinWriter()
-	stackitem.EncodeBinary(c.toStackItem(), w.BinWriter)
-	return w.Bytes()
-}
-
 // FromBytes unmarshals candidate from byte array.
 func (c *candidate) FromBytes(data []byte) *candidate {
-	r := io.NewBinReaderFromBuf(data)
-	item := stackitem.DecodeBinary(r)
-	if r.Err != nil {
-		panic(r.Err)
+	err := stackitem.DeserializeConvertible(data, c)
+	if err != nil {
+		panic(err)
 	}
-	return c.fromStackItem(item)
+	return c
 }
 
-func (c *candidate) toStackItem() stackitem.Item {
+// ToStackItem implements stackitem.Convertible. It never returns an error.
+func (c *candidate) ToStackItem() (stackitem.Item, error) {
 	return stackitem.NewStruct([]stackitem.Item{
 		stackitem.NewBool(c.Registered),
 		stackitem.NewBigInteger(&c.Votes),
-	})
+	}), nil
 }
 
-func (c *candidate) fromStackItem(item stackitem.Item) *candidate {
+// FromStackItem implements stackitem.Convertible.
+func (c *candidate) FromStackItem(item stackitem.Item) error {
 	arr := item.(*stackitem.Struct).Value().([]stackitem.Item)
 	vs, err := arr[1].TryInteger()
 	if err != nil {
-		panic(err)
+		return err
 	}
-	c.Registered, err = arr[0].TryBool()
+	reg, err := arr[0].TryBool()
 	if err != nil {
-		panic(err)
+		return err
 	}
+	c.Registered = reg
 	c.Votes = *vs
-	return c
+	return nil
 }
diff --git a/pkg/core/native/native_neo_test.go b/pkg/core/native/native_neo_test.go
index bccd3bd42..ebeb30742 100644
--- a/pkg/core/native/native_neo_test.go
+++ b/pkg/core/native/native_neo_test.go
@@ -4,7 +4,7 @@ import (
 	"math/big"
 	"testing"
 
-	"github.com/stretchr/testify/require"
+	"github.com/nspcc-dev/neo-go/internal/testserdes"
 )
 
 func TestCandidate_Bytes(t *testing.T) {
@@ -12,7 +12,6 @@ func TestCandidate_Bytes(t *testing.T) {
 		Registered: true,
 		Votes:      *big.NewInt(0x0F),
 	}
-	data := expected.Bytes()
-	actual := new(candidate).FromBytes(data)
-	require.Equal(t, expected, actual)
+	actual := new(candidate)
+	testserdes.ToFromStackItem(t, expected, actual)
 }
diff --git a/pkg/core/native/native_nep17.go b/pkg/core/native/native_nep17.go
index 0bf47a615..3a6612121 100644
--- a/pkg/core/native/native_nep17.go
+++ b/pkg/core/native/native_nep17.go
@@ -343,12 +343,12 @@ func toUint160(s stackitem.Item) util.Uint160 {
 
 func toUint32(s stackitem.Item) uint32 {
 	bigInt := toBigInt(s)
-	if !bigInt.IsInt64() {
-		panic("bigint is not an int64")
+	if !bigInt.IsUint64() {
+		panic("bigint is not an uint64")
 	}
-	int64Value := bigInt.Int64()
-	if int64Value < 0 || int64Value > math.MaxUint32 {
+	uint64Value := bigInt.Uint64()
+	if uint64Value > math.MaxUint32 {
 		panic("bigint does not fit into uint32")
 	}
-	return uint32(int64Value)
+	return uint32(uint64Value)
 }
diff --git a/pkg/core/native/neo_types.go b/pkg/core/native/neo_types.go
index 15dcf1e97..21e5dfb3b 100644
--- a/pkg/core/native/neo_types.go
+++ b/pkg/core/native/neo_types.go
@@ -6,7 +6,6 @@ import (
 	"math/big"
 
 	"github.com/nspcc-dev/neo-go/pkg/crypto/keys"
-	"github.com/nspcc-dev/neo-go/pkg/io"
 	"github.com/nspcc-dev/neo-go/pkg/vm/stackitem"
 )
 
@@ -84,21 +83,18 @@ func (k *keysWithVotes) fromStackItem(item stackitem.Item) error {
 
 // Bytes serializes keys with votes slice.
 func (k keysWithVotes) Bytes() []byte {
-	var it = k.toStackItem()
-	var w = io.NewBufBinWriter()
-	stackitem.EncodeBinary(it, w.BinWriter)
-	if w.Err != nil {
-		panic(w.Err)
+	buf, err := stackitem.Serialize(k.toStackItem())
+	if err != nil {
+		panic(err)
 	}
-	return w.Bytes()
+	return buf
 }
 
 // DecodeBytes deserializes keys and votes slice.
 func (k *keysWithVotes) DecodeBytes(data []byte) error {
-	var r = io.NewBinReaderFromBuf(data)
-	var it = stackitem.DecodeBinary(r)
-	if r.Err != nil {
-		return r.Err
+	it, err := stackitem.Deserialize(data)
+	if err != nil {
+		return err
 	}
 	return k.fromStackItem(it)
 }
diff --git a/pkg/core/native/notary.go b/pkg/core/native/notary.go
index e29224a0c..36d268a3e 100644
--- a/pkg/core/native/notary.go
+++ b/pkg/core/native/notary.go
@@ -414,7 +414,7 @@ func (n *Notary) setMaxNotValidBeforeDelta(ic *interop.Context, args []stackitem
 func (n *Notary) GetDepositFor(dao dao.DAO, acc util.Uint160) *state.Deposit {
 	key := append([]byte{prefixDeposit}, acc.BytesBE()...)
 	deposit := new(state.Deposit)
-	err := getSerializableFromDAO(n.ID, dao, key, deposit)
+	err := getConvertibleFromDAO(n.ID, dao, key, deposit)
 	if err == nil {
 		return deposit
 	}
@@ -427,7 +427,7 @@ func (n *Notary) GetDepositFor(dao dao.DAO, acc util.Uint160) *state.Deposit {
 // putDepositFor puts deposit on the balance of the specified account in the storage.
 func (n *Notary) putDepositFor(dao dao.DAO, deposit *state.Deposit, acc util.Uint160) error {
 	key := append([]byte{prefixDeposit}, acc.BytesBE()...)
-	return putSerializableToDAO(n.ID, dao, key, deposit)
+	return putConvertibleToDAO(n.ID, dao, key, deposit)
 }
 
 // removeDepositFor removes deposit from the storage.
diff --git a/pkg/core/native/oracle.go b/pkg/core/native/oracle.go
index 7c500f6cf..9f7ead2ac 100644
--- a/pkg/core/native/oracle.go
+++ b/pkg/core/native/oracle.go
@@ -170,7 +170,7 @@ func (o *Oracle) PostPersist(ic *interop.Context) error {
 		}
 		reqKey := makeRequestKey(resp.ID)
 		req := new(state.OracleRequest)
-		if err := o.getSerializableFromDAO(ic.DAO, reqKey, req); err != nil {
+		if err := o.getConvertibleFromDAO(ic.DAO, reqKey, req); err != nil {
 			continue
 		}
 		if err := ic.DAO.DeleteStorageItem(o.ID, reqKey); err != nil {
@@ -182,7 +182,7 @@ func (o *Oracle) PostPersist(ic *interop.Context) error {
 
 		idKey := makeIDListKey(req.URL)
 		idList := new(IDList)
-		if err := o.getSerializableFromDAO(ic.DAO, idKey, idList); err != nil {
+		if err := o.getConvertibleFromDAO(ic.DAO, idKey, idList); err != nil {
 			return err
 		}
 		if !idList.Remove(resp.ID) {
@@ -193,7 +193,7 @@ func (o *Oracle) PostPersist(ic *interop.Context) error {
 		if len(*idList) == 0 {
 			err = ic.DAO.DeleteStorageItem(o.ID, idKey)
 		} else {
-			err = ic.DAO.PutStorageItem(o.ID, idKey, idList.Bytes())
+			err = putConvertibleToDAO(o.ID, ic.DAO, idKey, idList)
 		}
 		if err != nil {
 			return err
@@ -277,11 +277,13 @@ func (o *Oracle) FinishInternal(ic *interop.Context) error {
 		}),
 	})
 
-	r := io.NewBinReaderFromBuf(req.UserData)
-	userData := stackitem.DecodeBinary(r)
+	userData, err := stackitem.Deserialize(req.UserData)
+	if err != nil {
+		return err
+	}
 	args := []stackitem.Item{
 		stackitem.Make(req.URL),
-		stackitem.Make(userData),
+		userData,
 		stackitem.Make(resp.Code),
 		stackitem.Make(resp.Result),
 	}
@@ -327,10 +329,10 @@ func (o *Oracle) request(ic *interop.Context, args []stackitem.Item) stackitem.I
 
 // RequestInternal processes oracle request.
 func (o *Oracle) RequestInternal(ic *interop.Context, url string, filter *string, cb string, userData stackitem.Item, gas *big.Int) error {
-	if len(url) > maxURLLength || (filter != nil && len(*filter) > maxFilterLength) || len(cb) > maxCallbackLength {
+	if len(url) > maxURLLength || (filter != nil && len(*filter) > maxFilterLength) || len(cb) > maxCallbackLength || !gas.IsInt64() {
 		return ErrBigArgument
 	}
-	if gas.Uint64() < MinimumResponseGas {
+	if gas.Int64() < MinimumResponseGas {
 		return ErrLowResponseGas
 	}
 	if strings.HasPrefix(cb, "_") {
@@ -357,12 +359,10 @@ func (o *Oracle) RequestInternal(ic *interop.Context, url string, filter *string
 		return err
 	}
 
-	w := io.NewBufBinWriter()
-	stackitem.EncodeBinary(userData, w.BinWriter)
-	if w.Err != nil {
-		return w.Err
+	data, err := stackitem.Serialize(userData)
+	if err != nil {
+		return err
 	}
-	data := w.Bytes()
 	if len(data) > maxUserDataLength {
 		return ErrBigArgument
 	}
@@ -398,7 +398,7 @@ func (o *Oracle) RequestInternal(ic *interop.Context, url string, filter *string
 // PutRequestInternal puts oracle request with the specified id to d.
 func (o *Oracle) PutRequestInternal(id uint64, req *state.OracleRequest, d dao.DAO) error {
 	reqKey := makeRequestKey(id)
-	if err := d.PutStorageItem(o.ID, reqKey, req.Bytes()); err != nil {
+	if err := putConvertibleToDAO(o.ID, d, reqKey, req); err != nil {
 		return err
 	}
 	o.newRequests[id] = req
@@ -406,14 +406,14 @@ func (o *Oracle) PutRequestInternal(id uint64, req *state.OracleRequest, d dao.D
 	// Add request ID to the id list.
 	lst := new(IDList)
 	key := makeIDListKey(req.URL)
-	if err := o.getSerializableFromDAO(d, key, lst); err != nil && !errors.Is(err, storage.ErrKeyNotFound) {
+	if err := o.getConvertibleFromDAO(d, key, lst); err != nil && !errors.Is(err, storage.ErrKeyNotFound) {
 		return err
 	}
 	if len(*lst) >= maxRequestsCount {
 		return fmt.Errorf("there are too many pending requests for %s url", req.URL)
 	}
 	*lst = append(*lst, id)
-	return d.PutStorageItem(o.ID, key, lst.Bytes())
+	return putConvertibleToDAO(o.ID, d, key, lst)
 }
 
 // GetScriptHash returns script hash or oracle nodes.
@@ -431,14 +431,14 @@ func (o *Oracle) GetOracleNodes(d dao.DAO) (keys.PublicKeys, error) {
 func (o *Oracle) GetRequestInternal(d dao.DAO, id uint64) (*state.OracleRequest, error) {
 	key := makeRequestKey(id)
 	req := new(state.OracleRequest)
-	return req, o.getSerializableFromDAO(d, key, req)
+	return req, o.getConvertibleFromDAO(d, key, req)
 }
 
 // GetIDListInternal returns request by ID and key under which it is stored.
 func (o *Oracle) GetIDListInternal(d dao.DAO, url string) (*IDList, error) {
 	key := makeIDListKey(url)
 	idList := new(IDList)
-	return idList, o.getSerializableFromDAO(d, key, idList)
+	return idList, o.getConvertibleFromDAO(d, key, idList)
 }
 
 func (o *Oracle) verify(ic *interop.Context, _ []stackitem.Item) stackitem.Item {
@@ -493,11 +493,10 @@ func (o *Oracle) getRequests(d dao.DAO) (map[uint64]*state.OracleRequest, error)
 		if len(k) != 8 {
 			return nil, errors.New("invalid request ID")
 		}
-		r := io.NewBinReaderFromBuf(si)
 		req := new(state.OracleRequest)
-		req.DecodeBinary(r)
-		if r.Err != nil {
-			return nil, r.Err
+		err = stackitem.DeserializeConvertible(si, req)
+		if err != nil {
+			return nil, err
 		}
 		id := binary.BigEndian.Uint64([]byte(k))
 		reqs[id] = req
@@ -516,8 +515,8 @@ func makeIDListKey(url string) []byte {
 	return append(prefixIDList, hash.Hash160([]byte(url)).BytesBE()...)
 }
 
-func (o *Oracle) getSerializableFromDAO(d dao.DAO, key []byte, item io.Serializable) error {
-	return getSerializableFromDAO(o.ID, d, key, item)
+func (o *Oracle) getConvertibleFromDAO(d dao.DAO, key []byte, item stackitem.Convertible) error {
+	return getConvertibleFromDAO(o.ID, d, key, item)
 }
 
 // updateCache updates cached Oracle values if they've been changed.
diff --git a/pkg/core/native/oracle_types.go b/pkg/core/native/oracle_types.go
index 985897e72..b678f67db 100644
--- a/pkg/core/native/oracle_types.go
+++ b/pkg/core/native/oracle_types.go
@@ -6,7 +6,6 @@ import (
 	"math/big"
 
 	"github.com/nspcc-dev/neo-go/pkg/crypto/keys"
-	"github.com/nspcc-dev/neo-go/pkg/io"
 	"github.com/nspcc-dev/neo-go/pkg/vm/stackitem"
 )
 
@@ -16,36 +15,17 @@ type IDList []uint64
 // NodeList represents list or oracle nodes.
 type NodeList keys.PublicKeys
 
-// Bytes return l serizalized to a byte-slice.
-func (l IDList) Bytes() []byte {
-	w := io.NewBufBinWriter()
-	l.EncodeBinary(w.BinWriter)
-	return w.Bytes()
-}
-
-// EncodeBinary implements io.Serializable.
-func (l IDList) EncodeBinary(w *io.BinWriter) {
-	stackitem.EncodeBinary(l.toStackItem(), w)
-}
-
-// DecodeBinary implements io.Serializable.
-func (l *IDList) DecodeBinary(r *io.BinReader) {
-	item := stackitem.DecodeBinary(r)
-	if r.Err != nil || item == nil {
-		return
-	}
-	r.Err = l.fromStackItem(item)
-}
-
-func (l IDList) toStackItem() stackitem.Item {
+// ToStackItem implements stackitem.Convertible. It never returns an error.
+func (l IDList) ToStackItem() (stackitem.Item, error) {
 	arr := make([]stackitem.Item, len(l))
 	for i := range l {
 		arr[i] = stackitem.NewBigInteger(new(big.Int).SetUint64(l[i]))
 	}
-	return stackitem.NewArray(arr)
+	return stackitem.NewArray(arr), nil
 }
 
-func (l *IDList) fromStackItem(it stackitem.Item) error {
+// FromStackItem implements stackitem.Convertible.
+func (l *IDList) FromStackItem(it stackitem.Item) error {
 	arr, ok := it.Value().([]stackitem.Item)
 	if !ok {
 		return errors.New("not an array")
@@ -75,36 +55,17 @@ func (l *IDList) Remove(id uint64) bool {
 	return false
 }
 
-// Bytes return l serizalized to a byte-slice.
-func (l NodeList) Bytes() []byte {
-	w := io.NewBufBinWriter()
-	l.EncodeBinary(w.BinWriter)
-	return w.Bytes()
-}
-
-// EncodeBinary implements io.Serializable.
-func (l NodeList) EncodeBinary(w *io.BinWriter) {
-	stackitem.EncodeBinary(l.toStackItem(), w)
-}
-
-// DecodeBinary implements io.Serializable.
-func (l *NodeList) DecodeBinary(r *io.BinReader) {
-	item := stackitem.DecodeBinary(r)
-	if r.Err != nil || item == nil {
-		return
-	}
-	r.Err = l.fromStackItem(item)
-}
-
-func (l NodeList) toStackItem() stackitem.Item {
+// ToStackItem implements stackitem.Convertible. It never returns an error.
+func (l NodeList) ToStackItem() (stackitem.Item, error) {
 	arr := make([]stackitem.Item, len(l))
 	for i := range l {
 		arr[i] = stackitem.NewByteArray(l[i].Bytes())
 	}
-	return stackitem.NewArray(arr)
+	return stackitem.NewArray(arr), nil
 }
 
-func (l *NodeList) fromStackItem(it stackitem.Item) error {
+// FromStackItem implements stackitem.Convertible.
+func (l *NodeList) FromStackItem(it stackitem.Item) error {
 	arr, ok := it.Value().([]stackitem.Item)
 	if !ok {
 		return errors.New("not an array")
diff --git a/pkg/core/native/oracle_types_test.go b/pkg/core/native/oracle_types_test.go
index c58323dd9..cba0e20b1 100644
--- a/pkg/core/native/oracle_types_test.go
+++ b/pkg/core/native/oracle_types_test.go
@@ -5,32 +5,26 @@ import (
 
 	"github.com/nspcc-dev/neo-go/internal/testserdes"
 	"github.com/nspcc-dev/neo-go/pkg/crypto/keys"
-	"github.com/nspcc-dev/neo-go/pkg/io"
 	"github.com/nspcc-dev/neo-go/pkg/vm/stackitem"
 	"github.com/stretchr/testify/require"
 )
 
-func getInvalidTestFunc(actual io.Serializable, value interface{}) func(t *testing.T) {
+func getInvalidTestFunc(actual stackitem.Convertible, value interface{}) func(t *testing.T) {
 	return func(t *testing.T) {
-		w := io.NewBufBinWriter()
 		it := stackitem.Make(value)
-		stackitem.EncodeBinary(it, w.BinWriter)
-		require.NoError(t, w.Err)
-		require.Error(t, testserdes.DecodeBinary(w.Bytes(), actual))
+		require.Error(t, actual.FromStackItem(it))
 	}
 }
 
-func TestIDList_EncodeBinary(t *testing.T) {
+func TestIDListToFromSI(t *testing.T) {
 	t.Run("Valid", func(t *testing.T) {
 		l := &IDList{1, 4, 5}
-		testserdes.EncodeDecodeBinary(t, l, new(IDList))
+		var l2 = new(IDList)
+		testserdes.ToFromStackItem(t, l, l2)
 	})
 	t.Run("Invalid", func(t *testing.T) {
 		t.Run("NotArray", getInvalidTestFunc(new(IDList), []byte{}))
 		t.Run("InvalidElement", getInvalidTestFunc(new(IDList), []stackitem.Item{stackitem.Null{}}))
-		t.Run("NotStackItem", func(t *testing.T) {
-			require.Error(t, testserdes.DecodeBinary([]byte{0x77}, new(IDList)))
-		})
 	})
 }
 
@@ -50,22 +44,20 @@ func TestIDList_Remove(t *testing.T) {
 	require.Equal(t, IDList{1}, l)
 }
 
-func TestNodeList_EncodeBinary(t *testing.T) {
+func TestNodeListToFromSI(t *testing.T) {
 	priv, err := keys.NewPrivateKey()
 	require.NoError(t, err)
 	pub := priv.PublicKey()
 
 	t.Run("Valid", func(t *testing.T) {
 		l := &NodeList{pub}
-		testserdes.EncodeDecodeBinary(t, l, new(NodeList))
+		var l2 = new(NodeList)
+		testserdes.ToFromStackItem(t, l, l2)
 	})
 	t.Run("Invalid", func(t *testing.T) {
 		t.Run("NotArray", getInvalidTestFunc(new(NodeList), []byte{}))
 		t.Run("InvalidElement", getInvalidTestFunc(new(NodeList), []stackitem.Item{stackitem.Null{}}))
 		t.Run("InvalidKey", getInvalidTestFunc(new(NodeList),
 			[]stackitem.Item{stackitem.NewByteArray([]byte{0x9})}))
-		t.Run("NotStackItem", func(t *testing.T) {
-			require.Error(t, testserdes.DecodeBinary([]byte{0x77}, new(NodeList)))
-		})
 	})
 }
diff --git a/pkg/core/native/std_test.go b/pkg/core/native/std_test.go
index 2558b5f2d..2817850e0 100644
--- a/pkg/core/native/std_test.go
+++ b/pkg/core/native/std_test.go
@@ -11,7 +11,6 @@ import (
 	"github.com/mr-tron/base58"
 	"github.com/nspcc-dev/neo-go/pkg/core/interop"
 	base58neogo "github.com/nspcc-dev/neo-go/pkg/encoding/base58"
-	"github.com/nspcc-dev/neo-go/pkg/io"
 	"github.com/nspcc-dev/neo-go/pkg/vm"
 	"github.com/nspcc-dev/neo-go/pkg/vm/stackitem"
 	"github.com/stretchr/testify/assert"
@@ -275,11 +274,8 @@ func TestStdLibSerialize(t *testing.T) {
 			actualSerialized = s.serialize(ic, []stackitem.Item{stackitem.Make(42)})
 		})
 
-		w := io.NewBufBinWriter()
-		stackitem.EncodeBinary(stackitem.Make(42), w.BinWriter)
-		require.NoError(t, w.Err)
-
-		encoded := w.Bytes()
+		encoded, err := stackitem.Serialize(stackitem.Make(42))
+		require.NoError(t, err)
 		require.Equal(t, stackitem.Make(encoded), actualSerialized)
 
 		require.NotPanics(t, func() {
diff --git a/pkg/core/native/util.go b/pkg/core/native/util.go
index c882762cb..afb20728c 100644
--- a/pkg/core/native/util.go
+++ b/pkg/core/native/util.go
@@ -8,30 +8,26 @@ import (
 	"github.com/nspcc-dev/neo-go/pkg/core/dao"
 	"github.com/nspcc-dev/neo-go/pkg/core/storage"
 	"github.com/nspcc-dev/neo-go/pkg/encoding/bigint"
-	"github.com/nspcc-dev/neo-go/pkg/io"
 	"github.com/nspcc-dev/neo-go/pkg/util"
 	"github.com/nspcc-dev/neo-go/pkg/vm/stackitem"
 )
 
 var intOne = big.NewInt(1)
 
-func getSerializableFromDAO(id int32, d dao.DAO, key []byte, item io.Serializable) error {
+func getConvertibleFromDAO(id int32, d dao.DAO, key []byte, conv stackitem.Convertible) error {
 	si := d.GetStorageItem(id, key)
 	if si == nil {
 		return storage.ErrKeyNotFound
 	}
-	r := io.NewBinReaderFromBuf(si)
-	item.DecodeBinary(r)
-	return r.Err
+	return stackitem.DeserializeConvertible(si, conv)
 }
 
-func putSerializableToDAO(id int32, d dao.DAO, key []byte, item io.Serializable) error {
-	w := io.NewBufBinWriter()
-	item.EncodeBinary(w.BinWriter)
-	if w.Err != nil {
-		return w.Err
+func putConvertibleToDAO(id int32, d dao.DAO, key []byte, conv stackitem.Convertible) error {
+	data, err := stackitem.SerializeConvertible(conv)
+	if err != nil {
+		return err
 	}
-	return d.PutStorageItem(id, key, w.Bytes())
+	return d.PutStorageItem(id, key, data)
 }
 
 func setIntWithKey(id int32, dao dao.DAO, key []byte, value int64) error {
diff --git a/pkg/core/state/contract.go b/pkg/core/state/contract.go
index e6ee4e873..9d7cf8514 100644
--- a/pkg/core/state/contract.go
+++ b/pkg/core/state/contract.go
@@ -35,25 +35,6 @@ type NativeContract struct {
 	UpdateHistory []uint32 `json:"updatehistory"`
 }
 
-// DecodeBinary implements Serializable interface.
-func (c *Contract) DecodeBinary(r *io.BinReader) {
-	si := stackitem.DecodeBinary(r)
-	if r.Err != nil {
-		return
-	}
-	r.Err = c.FromStackItem(si)
-}
-
-// EncodeBinary implements Serializable interface.
-func (c *Contract) EncodeBinary(w *io.BinWriter) {
-	si, err := c.ToStackItem()
-	if err != nil {
-		w.Err = err
-		return
-	}
-	stackitem.EncodeBinary(si, w)
-}
-
 // ToStackItem converts state.Contract to stackitem.Item.
 func (c *Contract) ToStackItem() (stackitem.Item, error) {
 	rawNef, err := c.NEF.Bytes()
@@ -92,10 +73,10 @@ func (c *Contract) FromStackItem(item stackitem.Item) error {
 	if !ok {
 		return errors.New("UpdateCounter is not an integer")
 	}
-	if !bi.IsInt64() || bi.Int64() > math.MaxUint16 || bi.Int64() < 0 {
+	if !bi.IsUint64() || bi.Uint64() > math.MaxUint16 {
 		return errors.New("UpdateCounter not in uint16 range")
 	}
-	c.UpdateCounter = uint16(bi.Int64())
+	c.UpdateCounter = uint16(bi.Uint64())
 	bytes, err := arr[2].TryBytes()
 	if err != nil {
 		return err
diff --git a/pkg/core/state/contract_test.go b/pkg/core/state/contract_test.go
index d2c7987ec..3f872974a 100644
--- a/pkg/core/state/contract_test.go
+++ b/pkg/core/state/contract_test.go
@@ -14,7 +14,7 @@ import (
 	"github.com/stretchr/testify/require"
 )
 
-func TestEncodeDecodeContractState(t *testing.T) {
+func TestContractStateToFromSI(t *testing.T) {
 	script := []byte("testscript")
 
 	h := hash.Hash160(script)
@@ -52,9 +52,9 @@ func TestEncodeDecodeContractState(t *testing.T) {
 	}
 	contract.NEF.Checksum = contract.NEF.CalculateChecksum()
 
-	t.Run("Serializable", func(t *testing.T) {
+	t.Run("Convertible", func(t *testing.T) {
 		contractDecoded := new(Contract)
-		testserdes.EncodeDecodeBinary(t, contract, contractDecoded)
+		testserdes.ToFromStackItem(t, contract, contractDecoded)
 	})
 	t.Run("JSON", func(t *testing.T) {
 		contractDecoded := new(Contract)
diff --git a/pkg/core/state/deposit.go b/pkg/core/state/deposit.go
index 8e45e9595..59c97fe54 100644
--- a/pkg/core/state/deposit.go
+++ b/pkg/core/state/deposit.go
@@ -1,10 +1,12 @@
 package state
 
 import (
+	"errors"
+	"fmt"
+	"math"
 	"math/big"
 
-	"github.com/nspcc-dev/neo-go/pkg/encoding/bigint"
-	"github.com/nspcc-dev/neo-go/pkg/io"
+	"github.com/nspcc-dev/neo-go/pkg/vm/stackitem"
 )
 
 // Deposit represents GAS deposit from Notary contract.
@@ -13,14 +15,37 @@ type Deposit struct {
 	Till   uint32
 }
 
-// EncodeBinary implements io.Serializable interface.
-func (d *Deposit) EncodeBinary(w *io.BinWriter) {
-	w.WriteVarBytes(bigint.ToBytes(d.Amount))
-	w.WriteU32LE(d.Till)
+// ToStackItem implements stackitem.Convertible interface. It never returns an
+// error.
+func (d *Deposit) ToStackItem() (stackitem.Item, error) {
+	return stackitem.NewStruct([]stackitem.Item{
+		stackitem.NewBigInteger(d.Amount),
+		stackitem.Make(d.Till),
+	}), nil
 }
 
-// DecodeBinary implements io.Serializable interface.
-func (d *Deposit) DecodeBinary(r *io.BinReader) {
-	d.Amount = bigint.FromBytes(r.ReadVarBytes())
-	d.Till = r.ReadU32LE()
+// FromStackItem implements stackitem.Convertible interface.
+func (d *Deposit) FromStackItem(it stackitem.Item) error {
+	items, ok := it.Value().([]stackitem.Item)
+	if !ok {
+		return errors.New("not a struct")
+	}
+	if len(items) != 2 {
+		return errors.New("wrong number of elements")
+	}
+	amount, err := items[0].TryInteger()
+	if err != nil {
+		return fmt.Errorf("invalid amount: %w", err)
+	}
+	till, err := items[1].TryInteger()
+	if err != nil {
+		return fmt.Errorf("invalid till: %w", err)
+	}
+	tiu64 := till.Uint64()
+	if !till.IsUint64() || tiu64 > math.MaxUint32 {
+		return errors.New("wrong till value")
+	}
+	d.Amount = amount
+	d.Till = uint32(tiu64)
+	return nil
 }
diff --git a/pkg/core/state/deposit_test.go b/pkg/core/state/deposit_test.go
new file mode 100644
index 000000000..0b19052e6
--- /dev/null
+++ b/pkg/core/state/deposit_test.go
@@ -0,0 +1,54 @@
+package state
+
+import (
+	"math/big"
+	"testing"
+
+	"github.com/nspcc-dev/neo-go/internal/testserdes"
+	"github.com/nspcc-dev/neo-go/pkg/vm/stackitem"
+	"github.com/stretchr/testify/require"
+)
+
+func TestEncodeDecodeDeposit(t *testing.T) {
+	d := &Deposit{Amount: big.NewInt(100500), Till: 888}
+	depo := new(Deposit)
+	testserdes.ToFromStackItem(t, d, depo)
+}
+
+func TestDepositFromStackItem(t *testing.T) {
+	var d Deposit
+
+	item := stackitem.Make(42)
+	require.Error(t, d.FromStackItem(item))
+
+	item = stackitem.NewStruct(nil)
+	require.Error(t, d.FromStackItem(item))
+
+	item = stackitem.NewStruct([]stackitem.Item{
+		stackitem.NewStruct(nil),
+		stackitem.NewStruct(nil),
+	})
+	require.Error(t, d.FromStackItem(item))
+
+	item = stackitem.NewStruct([]stackitem.Item{
+		stackitem.Make(777),
+		stackitem.NewStruct(nil),
+	})
+	require.Error(t, d.FromStackItem(item))
+
+	item = stackitem.NewStruct([]stackitem.Item{
+		stackitem.Make(777),
+		stackitem.Make(-1),
+	})
+	require.Error(t, d.FromStackItem(item))
+	item = stackitem.NewStruct([]stackitem.Item{
+		stackitem.Make(777),
+		stackitem.Make("somenonu64value"),
+	})
+	require.Error(t, d.FromStackItem(item))
+	item = stackitem.NewStruct([]stackitem.Item{
+		stackitem.Make(777),
+		stackitem.Make(888),
+	})
+	require.NoError(t, d.FromStackItem(item))
+}
diff --git a/pkg/core/state/native_state.go b/pkg/core/state/native_state.go
index 75baee89d..a4f652e3f 100644
--- a/pkg/core/state/native_state.go
+++ b/pkg/core/state/native_state.go
@@ -7,7 +7,6 @@ import (
 	"math/big"
 
 	"github.com/nspcc-dev/neo-go/pkg/crypto/keys"
-	"github.com/nspcc-dev/neo-go/pkg/io"
 	"github.com/nspcc-dev/neo-go/pkg/vm/stackitem"
 )
 
@@ -26,99 +25,81 @@ type NEOBalanceState struct {
 // NEP17BalanceStateFromBytes converts serialized NEP17BalanceState to structure.
 func NEP17BalanceStateFromBytes(b []byte) (*NEP17BalanceState, error) {
 	balance := new(NEP17BalanceState)
-	if len(b) == 0 {
-		return balance, nil
-	}
-	r := io.NewBinReaderFromBuf(b)
-	balance.DecodeBinary(r)
-	if r.Err != nil {
-		return nil, r.Err
+	err := balanceFromBytes(b, balance)
+	if err != nil {
+		return nil, err
 	}
 	return balance, nil
 }
 
 // Bytes returns serialized NEP17BalanceState.
 func (s *NEP17BalanceState) Bytes() []byte {
-	w := io.NewBufBinWriter()
-	s.EncodeBinary(w.BinWriter)
-	if w.Err != nil {
-		panic(w.Err)
+	return balanceToBytes(s)
+}
+
+func balanceFromBytes(b []byte, item stackitem.Convertible) error {
+	if len(b) == 0 {
+		return nil
 	}
-	return w.Bytes()
+	return stackitem.DeserializeConvertible(b, item)
 }
 
-func (s *NEP17BalanceState) toStackItem() stackitem.Item {
-	return stackitem.NewStruct([]stackitem.Item{stackitem.NewBigInteger(&s.Balance)})
-}
-
-func (s *NEP17BalanceState) fromStackItem(item stackitem.Item) {
-	s.Balance = *item.(*stackitem.Struct).Value().([]stackitem.Item)[0].Value().(*big.Int)
-}
-
-// EncodeBinary implements io.Serializable interface.
-func (s *NEP17BalanceState) EncodeBinary(w *io.BinWriter) {
-	si := s.toStackItem()
-	stackitem.EncodeBinary(si, w)
-}
-
-// DecodeBinary implements io.Serializable interface.
-func (s *NEP17BalanceState) DecodeBinary(r *io.BinReader) {
-	si := stackitem.DecodeBinary(r)
-	if r.Err != nil {
-		return
+func balanceToBytes(item stackitem.Convertible) []byte {
+	data, err := stackitem.SerializeConvertible(item)
+	if err != nil {
+		panic(err)
 	}
-	s.fromStackItem(si)
+	return data
+}
+
+// ToStackItem implements stackitem.Convertible. It never returns an error.
+func (s *NEP17BalanceState) ToStackItem() (stackitem.Item, error) {
+	return stackitem.NewStruct([]stackitem.Item{stackitem.NewBigInteger(&s.Balance)}), nil
+}
+
+// FromStackItem implements stackitem.Convertible.
+func (s *NEP17BalanceState) FromStackItem(item stackitem.Item) error {
+	items, ok := item.Value().([]stackitem.Item)
+	if !ok {
+		return errors.New("not a struct")
+	}
+	if len(items) < 1 {
+		return errors.New("no balance value")
+	}
+	balance, err := items[0].TryInteger()
+	if err != nil {
+		return fmt.Errorf("invalid balance: %w", err)
+	}
+	s.Balance = *balance
+	return nil
 }
 
 // NEOBalanceStateFromBytes converts serialized NEOBalanceState to structure.
 func NEOBalanceStateFromBytes(b []byte) (*NEOBalanceState, error) {
 	balance := new(NEOBalanceState)
-	if len(b) == 0 {
-		return balance, nil
-	}
-	r := io.NewBinReaderFromBuf(b)
-	balance.DecodeBinary(r)
-
-	if r.Err != nil {
-		return nil, r.Err
+	err := balanceFromBytes(b, balance)
+	if err != nil {
+		return nil, err
 	}
 	return balance, nil
 }
 
 // Bytes returns serialized NEOBalanceState.
 func (s *NEOBalanceState) Bytes() []byte {
-	w := io.NewBufBinWriter()
-	s.EncodeBinary(w.BinWriter)
-	if w.Err != nil {
-		panic(w.Err)
-	}
-	return w.Bytes()
+	return balanceToBytes(s)
 }
 
-// EncodeBinary implements io.Serializable interface.
-func (s *NEOBalanceState) EncodeBinary(w *io.BinWriter) {
-	si := s.toStackItem()
-	stackitem.EncodeBinary(si, w)
-}
-
-// DecodeBinary implements io.Serializable interface.
-func (s *NEOBalanceState) DecodeBinary(r *io.BinReader) {
-	si := stackitem.DecodeBinary(r)
-	if r.Err != nil {
-		return
-	}
-	r.Err = s.FromStackItem(si)
-}
-
-func (s *NEOBalanceState) toStackItem() stackitem.Item {
-	result := s.NEP17BalanceState.toStackItem().(*stackitem.Struct)
+// ToStackItem implements stackitem.Convertible interface. It never returns an error.
+func (s *NEOBalanceState) ToStackItem() (stackitem.Item, error) {
+	resItem, _ := s.NEP17BalanceState.ToStackItem()
+	result := resItem.(*stackitem.Struct)
 	result.Append(stackitem.NewBigInteger(big.NewInt(int64(s.BalanceHeight))))
 	if s.VoteTo != nil {
 		result.Append(stackitem.NewByteArray(s.VoteTo.Bytes()))
 	} else {
 		result.Append(stackitem.Null{})
 	}
-	return result
+	return result, nil
 }
 
 // FromStackItem converts stackitem.Item to NEOBalanceState.
diff --git a/pkg/core/state/notification_event.go b/pkg/core/state/notification_event.go
index 87ea9dbb1..5c7962ca0 100644
--- a/pkg/core/state/notification_event.go
+++ b/pkg/core/state/notification_event.go
@@ -72,7 +72,7 @@ func (aer *AppExecResult) DecodeBinary(r *io.BinReader) {
 	aer.VMState = vm.State(r.ReadB())
 	aer.GasConsumed = int64(r.ReadU64LE())
 	sz := r.ReadVarUint()
-	if stackitem.MaxArraySize < sz && r.Err == nil {
+	if stackitem.MaxDeserialized < sz && r.Err == nil {
 		r.Err = errors.New("invalid format")
 	}
 	if r.Err != nil {
diff --git a/pkg/core/state/oracle.go b/pkg/core/state/oracle.go
index 96efde901..861a5a1db 100644
--- a/pkg/core/state/oracle.go
+++ b/pkg/core/state/oracle.go
@@ -5,7 +5,6 @@ import (
 	"math/big"
 	"unicode/utf8"
 
-	"github.com/nspcc-dev/neo-go/pkg/io"
 	"github.com/nspcc-dev/neo-go/pkg/util"
 	"github.com/nspcc-dev/neo-go/pkg/vm/stackitem"
 )
@@ -21,28 +20,9 @@ type OracleRequest struct {
 	UserData         []byte
 }
 
-// Bytes return o serizalized to a byte-slice.
-func (o *OracleRequest) Bytes() []byte {
-	w := io.NewBufBinWriter()
-	o.EncodeBinary(w.BinWriter)
-	return w.Bytes()
-}
-
-// EncodeBinary implements io.Serializable.
-func (o *OracleRequest) EncodeBinary(w *io.BinWriter) {
-	stackitem.EncodeBinary(o.toStackItem(), w)
-}
-
-// DecodeBinary implements io.Serializable.
-func (o *OracleRequest) DecodeBinary(r *io.BinReader) {
-	item := stackitem.DecodeBinary(r)
-	if r.Err != nil || item == nil {
-		return
-	}
-	r.Err = o.fromStackItem(item)
-}
-
-func (o *OracleRequest) toStackItem() stackitem.Item {
+// ToStackItem implements stackitem.Convertible interface. It never returns an
+// error.
+func (o *OracleRequest) ToStackItem() (stackitem.Item, error) {
 	filter := stackitem.Item(stackitem.Null{})
 	if o.Filter != nil {
 		filter = stackitem.Make(*o.Filter)
@@ -55,10 +35,11 @@ func (o *OracleRequest) toStackItem() stackitem.Item {
 		stackitem.NewByteArray(o.CallbackContract.BytesBE()),
 		stackitem.Make(o.CallbackMethod),
 		stackitem.NewByteArray(o.UserData),
-	})
+	}), nil
 }
 
-func (o *OracleRequest) fromStackItem(it stackitem.Item) error {
+// FromStackItem implements stackitem.Convertible interface.
+func (o *OracleRequest) FromStackItem(it stackitem.Item) error {
 	arr, ok := it.Value().([]stackitem.Item)
 	if !ok || len(arr) < 7 {
 		return errors.New("not an array of needed length")
diff --git a/pkg/core/state/oracle_test.go b/pkg/core/state/oracle_test.go
index bb17ee6bc..07e2ce1f6 100644
--- a/pkg/core/state/oracle_test.go
+++ b/pkg/core/state/oracle_test.go
@@ -6,12 +6,11 @@ import (
 
 	"github.com/nspcc-dev/neo-go/internal/random"
 	"github.com/nspcc-dev/neo-go/internal/testserdes"
-	"github.com/nspcc-dev/neo-go/pkg/io"
 	"github.com/nspcc-dev/neo-go/pkg/vm/stackitem"
 	"github.com/stretchr/testify/require"
 )
 
-func TestOracleRequest_EncodeBinary(t *testing.T) {
+func TestOracleRequestToFromSI(t *testing.T) {
 	t.Run("Valid", func(t *testing.T) {
 		r := &OracleRequest{
 			OriginalTxID:     random.Uint256(),
@@ -21,25 +20,19 @@ func TestOracleRequest_EncodeBinary(t *testing.T) {
 			CallbackMethod:   "method",
 			UserData:         []byte{1, 2, 3},
 		}
-		testserdes.EncodeDecodeBinary(t, r, new(OracleRequest))
+		testserdes.ToFromStackItem(t, r, new(OracleRequest))
 
 		t.Run("WithFilter", func(t *testing.T) {
 			s := "filter"
 			r.Filter = &s
-			testserdes.EncodeDecodeBinary(t, r, new(OracleRequest))
+			testserdes.ToFromStackItem(t, r, new(OracleRequest))
 		})
 	})
 	t.Run("Invalid", func(t *testing.T) {
-		w := io.NewBufBinWriter()
+		var res = new(OracleRequest)
 		t.Run("NotArray", func(t *testing.T) {
-			w.Reset()
 			it := stackitem.NewByteArray([]byte{})
-			stackitem.EncodeBinary(it, w.BinWriter)
-			require.Error(t, testserdes.DecodeBinary(w.Bytes(), new(OracleRequest)))
-		})
-		t.Run("NotStackItem", func(t *testing.T) {
-			w.Reset()
-			require.Error(t, testserdes.DecodeBinary([]byte{0x77}, new(OracleRequest)))
+			require.Error(t, res.FromStackItem(it))
 		})
 
 		items := []stackitem.Item{
@@ -54,12 +47,10 @@ func TestOracleRequest_EncodeBinary(t *testing.T) {
 		arrItem := stackitem.NewArray(items)
 		runInvalid := func(i int, elem stackitem.Item) func(t *testing.T) {
 			return func(t *testing.T) {
-				w.Reset()
 				before := items[i]
 				items[i] = elem
-				stackitem.EncodeBinary(arrItem, w.BinWriter)
+				require.Error(t, res.FromStackItem(arrItem))
 				items[i] = before
-				require.Error(t, testserdes.DecodeBinary(w.Bytes(), new(OracleRequest)))
 			}
 		}
 		t.Run("TxID", func(t *testing.T) {
diff --git a/pkg/util/uint160_test.go b/pkg/util/uint160_test.go
index 7445242b1..f6bc855a2 100644
--- a/pkg/util/uint160_test.go
+++ b/pkg/util/uint160_test.go
@@ -1,21 +1,22 @@
-package util
+package util_test
 
 import (
 	"encoding/hex"
 	"testing"
 
 	"github.com/nspcc-dev/neo-go/internal/testserdes"
+	"github.com/nspcc-dev/neo-go/pkg/util"
 	"github.com/stretchr/testify/assert"
 	"github.com/stretchr/testify/require"
 )
 
 func TestUint160UnmarshalJSON(t *testing.T) {
 	str := "0263c1de100292813b5e075e585acc1bae963b2d"
-	expected, err := Uint160DecodeStringLE(str)
+	expected, err := util.Uint160DecodeStringLE(str)
 	assert.NoError(t, err)
 
 	// UnmarshalJSON decodes hex-strings
-	var u1, u2 Uint160
+	var u1, u2 util.Uint160
 
 	assert.NoError(t, u1.UnmarshalJSON([]byte(`"`+str+`"`)))
 	assert.True(t, expected.Equals(u1))
@@ -27,25 +28,25 @@ func TestUint160UnmarshalJSON(t *testing.T) {
 
 func TestUInt160DecodeString(t *testing.T) {
 	hexStr := "2d3b96ae1bcc5a585e075e3b81920210dec16302"
-	val, err := Uint160DecodeStringBE(hexStr)
+	val, err := util.Uint160DecodeStringBE(hexStr)
 	assert.NoError(t, err)
 	assert.Equal(t, hexStr, val.String())
 
-	valLE, err := Uint160DecodeStringLE(hexStr)
+	valLE, err := util.Uint160DecodeStringLE(hexStr)
 	assert.NoError(t, err)
 	assert.Equal(t, val, valLE.Reverse())
 
-	_, err = Uint160DecodeStringBE(hexStr[1:])
+	_, err = util.Uint160DecodeStringBE(hexStr[1:])
 	assert.Error(t, err)
 
-	_, err = Uint160DecodeStringLE(hexStr[1:])
+	_, err = util.Uint160DecodeStringLE(hexStr[1:])
 	assert.Error(t, err)
 
 	hexStr = "zz3b96ae1bcc5a585e075e3b81920210dec16302"
-	_, err = Uint160DecodeStringBE(hexStr)
+	_, err = util.Uint160DecodeStringBE(hexStr)
 	assert.Error(t, err)
 
-	_, err = Uint160DecodeStringLE(hexStr)
+	_, err = util.Uint160DecodeStringLE(hexStr)
 	assert.Error(t, err)
 }
 
@@ -54,18 +55,18 @@ func TestUint160DecodeBytes(t *testing.T) {
 	b, err := hex.DecodeString(hexStr)
 	require.NoError(t, err)
 
-	val, err := Uint160DecodeBytesBE(b)
+	val, err := util.Uint160DecodeBytesBE(b)
 	assert.NoError(t, err)
 	assert.Equal(t, hexStr, val.String())
 
-	valLE, err := Uint160DecodeBytesLE(b)
+	valLE, err := util.Uint160DecodeBytesLE(b)
 	assert.NoError(t, err)
 	assert.Equal(t, val, valLE.Reverse())
 
-	_, err = Uint160DecodeBytesLE(b[1:])
+	_, err = util.Uint160DecodeBytesLE(b[1:])
 	assert.Error(t, err)
 
-	_, err = Uint160DecodeBytesBE(b[1:])
+	_, err = util.Uint160DecodeBytesBE(b[1:])
 	assert.Error(t, err)
 }
 
@@ -73,10 +74,10 @@ func TestUInt160Equals(t *testing.T) {
 	a := "2d3b96ae1bcc5a585e075e3b81920210dec16302"
 	b := "4d3b96ae1bcc5a585e075e3b81920210dec16302"
 
-	ua, err := Uint160DecodeStringBE(a)
+	ua, err := util.Uint160DecodeStringBE(a)
 	require.NoError(t, err)
 
-	ub, err := Uint160DecodeStringBE(b)
+	ub, err := util.Uint160DecodeStringBE(b)
 	require.NoError(t, err)
 	assert.False(t, ua.Equals(ub), "%s and %s cannot be equal", ua, ub)
 	assert.True(t, ua.Equals(ua), "%s and %s must be equal", ua, ua)
@@ -86,11 +87,11 @@ func TestUInt160Less(t *testing.T) {
 	a := "2d3b96ae1bcc5a585e075e3b81920210dec16302"
 	b := "2d3b96ae1bcc5a585e075e3b81920210dec16303"
 
-	ua, err := Uint160DecodeStringBE(a)
+	ua, err := util.Uint160DecodeStringBE(a)
 	assert.Nil(t, err)
-	ua2, err := Uint160DecodeStringBE(a)
+	ua2, err := util.Uint160DecodeStringBE(a)
 	assert.Nil(t, err)
-	ub, err := Uint160DecodeStringBE(b)
+	ub, err := util.Uint160DecodeStringBE(b)
 	assert.Nil(t, err)
 	assert.Equal(t, true, ua.Less(ub))
 	assert.Equal(t, false, ua.Less(ua2))
@@ -101,7 +102,7 @@ func TestUInt160String(t *testing.T) {
 	hexStr := "b28427088a3729b2536d10122960394e8be6721f"
 	hexRevStr := "1f72e68b4e39602912106d53b229378a082784b2"
 
-	val, err := Uint160DecodeStringBE(hexStr)
+	val, err := util.Uint160DecodeStringBE(hexStr)
 	assert.Nil(t, err)
 
 	assert.Equal(t, hexStr, val.String())
@@ -110,7 +111,7 @@ func TestUInt160String(t *testing.T) {
 
 func TestUint160_Reverse(t *testing.T) {
 	hexStr := "b28427088a3729b2536d10122960394e8be6721f"
-	val, err := Uint160DecodeStringBE(hexStr)
+	val, err := util.Uint160DecodeStringBE(hexStr)
 
 	require.NoError(t, err)
 	assert.Equal(t, hexStr, val.Reverse().StringLE())
diff --git a/pkg/util/uint256_test.go b/pkg/util/uint256_test.go
index e0e3d2291..b1f5d2c3e 100644
--- a/pkg/util/uint256_test.go
+++ b/pkg/util/uint256_test.go
@@ -1,21 +1,22 @@
-package util
+package util_test
 
 import (
 	"encoding/hex"
 	"testing"
 
 	"github.com/nspcc-dev/neo-go/internal/testserdes"
+	"github.com/nspcc-dev/neo-go/pkg/util"
 	"github.com/stretchr/testify/assert"
 	"github.com/stretchr/testify/require"
 )
 
 func TestUint256UnmarshalJSON(t *testing.T) {
 	str := "f037308fa0ab18155bccfc08485468c112409ea5064595699e98c545f245f32d"
-	expected, err := Uint256DecodeStringLE(str)
+	expected, err := util.Uint256DecodeStringLE(str)
 	require.NoError(t, err)
 
 	// UnmarshalJSON decodes hex-strings
-	var u1, u2 Uint256
+	var u1, u2 util.Uint256
 
 	require.NoError(t, u1.UnmarshalJSON([]byte(`"`+str+`"`)))
 	assert.True(t, expected.Equals(u1))
@@ -28,33 +29,33 @@ func TestUint256UnmarshalJSON(t *testing.T) {
 
 func TestUint256DecodeString(t *testing.T) {
 	hexStr := "f037308fa0ab18155bccfc08485468c112409ea5064595699e98c545f245f32d"
-	val, err := Uint256DecodeStringLE(hexStr)
+	val, err := util.Uint256DecodeStringLE(hexStr)
 	require.NoError(t, err)
 	assert.Equal(t, hexStr, val.StringLE())
 
-	valBE, err := Uint256DecodeStringBE(hexStr)
+	valBE, err := util.Uint256DecodeStringBE(hexStr)
 	require.NoError(t, err)
 	assert.Equal(t, val, valBE.Reverse())
 
 	bs, err := hex.DecodeString(hexStr)
 	require.NoError(t, err)
 
-	val1, err := Uint256DecodeBytesBE(bs)
+	val1, err := util.Uint256DecodeBytesBE(bs)
 	assert.NoError(t, err)
 	assert.Equal(t, hexStr, val1.String())
 	assert.Equal(t, val, val1.Reverse())
 
-	_, err = Uint256DecodeStringLE(hexStr[1:])
+	_, err = util.Uint256DecodeStringLE(hexStr[1:])
 	assert.Error(t, err)
 
-	_, err = Uint256DecodeStringBE(hexStr[1:])
+	_, err = util.Uint256DecodeStringBE(hexStr[1:])
 	assert.Error(t, err)
 
 	hexStr = "zzz7308fa0ab18155bccfc08485468c112409ea5064595699e98c545f245f32d"
-	_, err = Uint256DecodeStringLE(hexStr)
+	_, err = util.Uint256DecodeStringLE(hexStr)
 	assert.Error(t, err)
 
-	_, err = Uint256DecodeStringBE(hexStr)
+	_, err = util.Uint256DecodeStringBE(hexStr)
 	assert.Error(t, err)
 }
 
@@ -63,11 +64,11 @@ func TestUint256DecodeBytes(t *testing.T) {
 	b, err := hex.DecodeString(hexStr)
 	require.NoError(t, err)
 
-	val, err := Uint256DecodeBytesLE(b)
+	val, err := util.Uint256DecodeBytesLE(b)
 	require.NoError(t, err)
 	assert.Equal(t, hexStr, val.StringLE())
 
-	_, err = Uint256DecodeBytesBE(b[1:])
+	_, err = util.Uint256DecodeBytesBE(b[1:])
 	assert.Error(t, err)
 }
 
@@ -75,10 +76,10 @@ func TestUInt256Equals(t *testing.T) {
 	a := "f037308fa0ab18155bccfc08485468c112409ea5064595699e98c545f245f32d"
 	b := "e287c5b29a1b66092be6803c59c765308ac20287e1b4977fd399da5fc8f66ab5"
 
-	ua, err := Uint256DecodeStringLE(a)
+	ua, err := util.Uint256DecodeStringLE(a)
 	require.NoError(t, err)
 
-	ub, err := Uint256DecodeStringLE(b)
+	ub, err := util.Uint256DecodeStringLE(b)
 	require.NoError(t, err)
 	assert.False(t, ua.Equals(ub), "%s and %s cannot be equal", ua, ub)
 	assert.True(t, ua.Equals(ua), "%s and %s must be equal", ua, ua)
@@ -86,11 +87,11 @@ func TestUInt256Equals(t *testing.T) {
 }
 
 func TestUint256_Serializable(t *testing.T) {
-	a := Uint256{
+	a := util.Uint256{
 		1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16,
 		17, 18, 19, 20, 21, 22, 23, 24, 25, 26, 27, 28, 29, 30, 31, 32,
 	}
 
-	var b Uint256
+	var b util.Uint256
 	testserdes.EncodeDecodeBinary(t, &a, &b)
 }
diff --git a/pkg/vm/contract_checks.go b/pkg/vm/contract_checks.go
index 9841ffb5b..40b7d6289 100644
--- a/pkg/vm/contract_checks.go
+++ b/pkg/vm/contract_checks.go
@@ -12,6 +12,9 @@ import (
 	"github.com/nspcc-dev/neo-go/pkg/vm/stackitem"
 )
 
+// MaxMultisigKeys is the maximum number of used keys for correct multisig contract.
+const MaxMultisigKeys = 1024
+
 var (
 	verifyInteropID   = interopnames.ToID([]byte(interopnames.SystemCryptoCheckSig))
 	multisigInteropID = interopnames.ToID([]byte(interopnames.SystemCryptoCheckMultisig))
@@ -25,14 +28,14 @@ func getNumOfThingsFromInstr(instr opcode.Opcode, param []byte) (int, bool) {
 		nthings = int(instr-opcode.PUSH1) + 1
 	case instr <= opcode.PUSHINT256:
 		n := bigint.FromBytes(param)
-		if !n.IsInt64() || n.Int64() > stackitem.MaxArraySize {
+		if !n.IsInt64() || n.Sign() < 0 || n.Int64() > MaxMultisigKeys {
 			return 0, false
 		}
 		nthings = int(n.Int64())
 	default:
 		return 0, false
 	}
-	if nthings < 1 || nthings > stackitem.MaxArraySize {
+	if nthings < 1 || nthings > MaxMultisigKeys {
 		return 0, false
 	}
 	return nthings, true
@@ -76,7 +79,7 @@ func ParseMultiSigContract(script []byte) (int, [][]byte, bool) {
 		}
 		pubs = append(pubs, param)
 		nkeys++
-		if nkeys > stackitem.MaxArraySize {
+		if nkeys > MaxMultisigKeys {
 			return nsigs, nil, false
 		}
 	}
diff --git a/pkg/vm/stackitem/item.go b/pkg/vm/stackitem/item.go
index c5d7007fe..3a156b22e 100644
--- a/pkg/vm/stackitem/item.go
+++ b/pkg/vm/stackitem/item.go
@@ -20,10 +20,12 @@ import (
 const (
 	// MaxBigIntegerSizeBits is the maximum size of BigInt item in bits.
 	MaxBigIntegerSizeBits = 32 * 8
-	// MaxArraySize is the maximum array size allowed in the VM.
-	MaxArraySize = 1024
 	// MaxSize is the maximum item size allowed in the VM.
 	MaxSize = 1024 * 1024
+	// MaxComparableNumOfItems is the maximum number of items that can be compared for structs.
+	MaxComparableNumOfItems = MaxDeserialized
+	// MaxClonableNumOfItems is the maximum number of items that can be cloned in structs.
+	MaxClonableNumOfItems = MaxDeserialized
 	// MaxByteArrayComparableSize is the maximum allowed length of ByteArray for Equals method.
 	// It is set to be the maximum uint16 value.
 	MaxByteArrayComparableSize = math.MaxUint16
@@ -52,6 +54,12 @@ type Item interface {
 	Convert(Type) (Item, error)
 }
 
+// Convertible is something that can be converted to/from Item.
+type Convertible interface {
+	ToStackItem() (Item, error)
+	FromStackItem(Item) error
+}
+
 var (
 	// ErrInvalidConversion is returned on attempt to make an incorrect
 	// conversion between item types.
@@ -67,6 +75,7 @@ var (
 	errTooBigInteger    = fmt.Errorf("%w: integer", ErrTooBig)
 	errTooBigKey        = fmt.Errorf("%w: map key", ErrTooBig)
 	errTooBigSize       = fmt.Errorf("%w: size", ErrTooBig)
+	errTooBigElements   = fmt.Errorf("%w: many elements", ErrTooBig)
 )
 
 // mkInvConversion creates conversion error with additional metadata (from and
@@ -260,17 +269,35 @@ func (i *Struct) TryInteger() (*big.Int, error) {
 
 // Equals implements Item interface.
 func (i *Struct) Equals(s Item) bool {
-	if i == s {
-		return true
-	} else if s == nil {
+	if s == nil {
 		return false
 	}
 	val, ok := s.(*Struct)
-	if !ok || len(i.value) != len(val.value) {
+	if !ok {
+		return false
+	}
+	var limit = MaxComparableNumOfItems - 1 // 1 for current element.
+	return i.equalStruct(val, &limit)
+}
+
+func (i *Struct) equalStruct(s *Struct, limit *int) bool {
+	if i == s {
+		return true
+	} else if len(i.value) != len(s.value) {
 		return false
 	}
 	for j := range i.value {
-		if !i.value[j].Equals(val.value[j]) {
+		*limit--
+		if *limit == 0 {
+			panic(errTooBigElements)
+		}
+		sa, oka := i.value[j].(*Struct)
+		sb, okb := s.value[j].(*Struct)
+		if oka && okb {
+			if !sa.equalStruct(sb, limit) {
+				return false
+			}
+		} else if !i.value[j].Equals(s.value[j]) {
 			return false
 		}
 	}
@@ -298,13 +325,18 @@ func (i *Struct) Convert(typ Type) (Item, error) {
 
 // Clone returns a Struct with all Struct fields copied by value.
 // Array fields are still copied by reference.
-func (i *Struct) Clone(limit int) (*Struct, error) {
+func (i *Struct) Clone() (*Struct, error) {
+	var limit = MaxClonableNumOfItems - 1 // For this struct itself.
 	return i.clone(&limit)
 }
 
 func (i *Struct) clone(limit *int) (*Struct, error) {
 	ret := &Struct{make([]Item, len(i.value))}
 	for j := range i.value {
+		*limit--
+		if *limit < 0 {
+			return nil, ErrTooBig
+		}
 		switch t := i.value[j].(type) {
 		case *Struct:
 			var err error
@@ -313,13 +345,9 @@ func (i *Struct) clone(limit *int) (*Struct, error) {
 			if err != nil {
 				return nil, err
 			}
-			*limit--
 		default:
 			ret.value[j] = t
 		}
-		if *limit < 0 {
-			return nil, ErrTooBig
-		}
 	}
 	return ret, nil
 }
diff --git a/pkg/vm/stackitem/item_test.go b/pkg/vm/stackitem/item_test.go
index 1244074a0..c114229ce 100644
--- a/pkg/vm/stackitem/item_test.go
+++ b/pkg/vm/stackitem/item_test.go
@@ -172,6 +172,11 @@ var equalsTestCases = map[string][]struct {
 			item2:  NewStruct([]Item{NewBigInteger(big.NewInt(1))}),
 			result: true,
 		},
+		{
+			item1:  NewStruct([]Item{NewBigInteger(big.NewInt(1)), NewStruct([]Item{})}),
+			item2:  NewStruct([]Item{NewBigInteger(big.NewInt(1)), NewStruct([]Item{})}),
+			result: true,
+		},
 	},
 	"bigint": {
 		{
@@ -381,6 +386,40 @@ func TestEquals(t *testing.T) {
 	}
 }
 
+func TestEqualsDeepStructure(t *testing.T) {
+	const perStruct = 4
+	var items = []Item{}
+	var num int
+	for i := 0; i < perStruct; i++ {
+		items = append(items, Make(0))
+		num++
+	}
+	var layerUp = func(sa *Struct, num int) (*Struct, int) {
+		items := []Item{}
+		for i := 0; i < perStruct; i++ {
+			clon, err := sa.Clone()
+			require.NoError(t, err)
+			items = append(items, clon)
+		}
+		num *= perStruct
+		num++
+		return NewStruct(items), num
+	}
+	var sa = NewStruct(items)
+	for i := 0; i < 4; i++ {
+		sa, num = layerUp(sa, num)
+	}
+	require.Less(t, num, MaxComparableNumOfItems)
+	sb, err := sa.Clone()
+	require.NoError(t, err)
+	require.True(t, sa.Equals(sb))
+	sa, num = layerUp(sa, num)
+	sb, num = layerUp(sb, num)
+
+	require.Less(t, MaxComparableNumOfItems, num)
+	require.Panics(t, func() { sa.Equals(sb) })
+}
+
 var marshalJSONTestCases = []struct {
 	input  Item
 	result []byte
@@ -468,9 +507,12 @@ func TestNewVeryBigInteger(t *testing.T) {
 func TestStructClone(t *testing.T) {
 	st0 := Struct{}
 	st := Struct{value: []Item{&st0}}
-	_, err := st.Clone(1)
-	require.NoError(t, err)
-	_, err = st.Clone(0)
+	for i := 0; i < MaxClonableNumOfItems-1; i++ {
+		nst, err := st.Clone()
+		require.NoError(t, err)
+		st = Struct{value: []Item{nst}}
+	}
+	_, err := st.Clone()
 	require.Error(t, err)
 }
 
diff --git a/pkg/vm/stackitem/serialization.go b/pkg/vm/stackitem/serialization.go
index 4fb5c2b56..b9a814e46 100644
--- a/pkg/vm/stackitem/serialization.go
+++ b/pkg/vm/stackitem/serialization.go
@@ -9,6 +9,10 @@ import (
 	"github.com/nspcc-dev/neo-go/pkg/io"
 )
 
+// MaxDeserialized is the maximum number one deserialized item can contain
+// (including itself).
+const MaxDeserialized = 2048
+
 // ErrRecursive is returned on attempts to serialize some recursive stack item
 // (like array including an item with reference to the same array).
 var ErrRecursive = errors.New("recursive item")
@@ -25,6 +29,13 @@ type serContext struct {
 	seen         map[Item]sliceNoPointer
 }
 
+// deserContext is an internal deserialization context.
+type deserContext struct {
+	*io.BinReader
+	allowInvalid bool
+	limit        int
+}
+
 // Serialize encodes given Item into the byte slice.
 func Serialize(item Item) ([]byte, error) {
 	sc := serContext{
@@ -179,21 +190,36 @@ func Deserialize(data []byte) (Item, error) {
 // as a function because Item itself is an interface. Caveat: always check
 // reader's error value before using the returned Item.
 func DecodeBinary(r *io.BinReader) Item {
-	return decodeBinary(r, false)
+	dc := deserContext{
+		BinReader:    r,
+		allowInvalid: false,
+		limit:        MaxDeserialized,
+	}
+	return dc.decodeBinary()
 }
 
 // DecodeBinaryProtected is similar to DecodeBinary but allows Interop and
 // Invalid values to be present (making it symmetric to EncodeBinaryProtected).
 func DecodeBinaryProtected(r *io.BinReader) Item {
-	return decodeBinary(r, true)
+	dc := deserContext{
+		BinReader:    r,
+		allowInvalid: true,
+		limit:        MaxDeserialized,
+	}
+	return dc.decodeBinary()
 }
 
-func decodeBinary(r *io.BinReader, allowInvalid bool) Item {
+func (r *deserContext) decodeBinary() Item {
 	var t = Type(r.ReadB())
 	if r.Err != nil {
 		return nil
 	}
 
+	r.limit--
+	if r.limit < 0 {
+		r.Err = errTooBigElements
+		return nil
+	}
 	switch t {
 	case ByteArrayT, BufferT:
 		data := r.ReadVarBytes(MaxSize)
@@ -210,9 +236,13 @@ func decodeBinary(r *io.BinReader, allowInvalid bool) Item {
 		return NewBigInteger(num)
 	case ArrayT, StructT:
 		size := int(r.ReadVarUint())
+		if size > MaxDeserialized {
+			r.Err = errTooBigElements
+			return nil
+		}
 		arr := make([]Item, size)
 		for i := 0; i < size; i++ {
-			arr[i] = DecodeBinary(r)
+			arr[i] = r.decodeBinary()
 		}
 
 		if t == ArrayT {
@@ -221,10 +251,14 @@ func decodeBinary(r *io.BinReader, allowInvalid bool) Item {
 		return NewStruct(arr)
 	case MapT:
 		size := int(r.ReadVarUint())
+		if size > MaxDeserialized {
+			r.Err = errTooBigElements
+			return nil
+		}
 		m := NewMap()
 		for i := 0; i < size; i++ {
-			key := DecodeBinary(r)
-			value := DecodeBinary(r)
+			key := r.decodeBinary()
+			value := r.decodeBinary()
 			if r.Err != nil {
 				break
 			}
@@ -234,15 +268,33 @@ func decodeBinary(r *io.BinReader, allowInvalid bool) Item {
 	case AnyT:
 		return Null{}
 	case InteropT:
-		if allowInvalid {
+		if r.allowInvalid {
 			return NewInterop(nil)
 		}
 		fallthrough
 	default:
-		if t == InvalidT && allowInvalid {
+		if t == InvalidT && r.allowInvalid {
 			return nil
 		}
 		r.Err = fmt.Errorf("%w: %v", ErrInvalidType, t)
 		return nil
 	}
 }
+
+// SerializeConvertible serializes Convertible into a slice of bytes.
+func SerializeConvertible(conv Convertible) ([]byte, error) {
+	item, err := conv.ToStackItem()
+	if err != nil {
+		return nil, err
+	}
+	return Serialize(item)
+}
+
+// DeserializeConvertible deserializes Convertible from a slice of bytes.
+func DeserializeConvertible(data []byte, conv Convertible) error {
+	item, err := Deserialize(data)
+	if err != nil {
+		return err
+	}
+	return conv.FromStackItem(item)
+}
diff --git a/pkg/vm/stackitem/serialization_test.go b/pkg/vm/stackitem/serialization_test.go
index b5adff651..139fbcbcf 100644
--- a/pkg/vm/stackitem/serialization_test.go
+++ b/pkg/vm/stackitem/serialization_test.go
@@ -39,6 +39,7 @@ func testSerialize(t *testing.T, expectedErr error, item Item) {
 func TestSerialize(t *testing.T) {
 	bigByteArray := NewByteArray(make([]byte, MaxSize/2))
 	smallByteArray := NewByteArray(make([]byte, MaxSize/4))
+	zeroByteArray := NewByteArray(make([]byte, 0))
 	testArray := func(t *testing.T, newItem func([]Item) Item) {
 		arr := newItem([]Item{bigByteArray})
 		testSerialize(t, nil, arr)
@@ -50,6 +51,18 @@ func TestSerialize(t *testing.T) {
 
 		arr.Value().([]Item)[0] = arr
 		testSerialize(t, ErrRecursive, arr)
+
+		items := make([]Item, 0, MaxDeserialized-1)
+		for i := 0; i < MaxDeserialized-1; i++ {
+			items = append(items, zeroByteArray)
+		}
+		testSerialize(t, nil, newItem(items))
+
+		items = append(items, zeroByteArray)
+		data, err := Serialize(newItem(items))
+		require.NoError(t, err)
+		_, err = Deserialize(data)
+		require.True(t, errors.Is(err, ErrTooBig), err)
 	}
 	t.Run("array", func(t *testing.T) {
 		testArray(t, func(items []Item) Item { return NewArray(items) })
@@ -126,9 +139,59 @@ func TestSerialize(t *testing.T) {
 		m.Add(Make(0), NewByteArray(make([]byte, MaxSize-MaxKeySize)))
 		m.Add(NewByteArray(make([]byte, MaxKeySize)), Make(1))
 		testSerialize(t, ErrTooBig, m)
+
+		m = NewMap()
+		for i := 0; i < MaxDeserialized/2-1; i++ {
+			m.Add(Make(i), zeroByteArray)
+		}
+		testSerialize(t, nil, m)
+
+		for i := 0; i <= MaxDeserialized; i++ {
+			m.Add(Make(i), zeroByteArray)
+		}
+		data, err := Serialize(m)
+		require.NoError(t, err)
+		_, err = Deserialize(data)
+		require.True(t, errors.Is(err, ErrTooBig), err)
 	})
 }
 
+func TestEmptyDeserialization(t *testing.T) {
+	empty := []byte{}
+	_, err := Deserialize(empty)
+	require.Error(t, err)
+}
+
+func TestMapDeserializationError(t *testing.T) {
+	m := NewMap()
+	m.Add(Make(1), Make(1))
+	m.Add(Make(2), nil) // Bad value
+	m.Add(Make(3), Make(3))
+
+	w := io.NewBufBinWriter()
+	EncodeBinaryProtected(m, w.BinWriter)
+	require.NoError(t, w.Err)
+	_, err := Deserialize(w.Bytes())
+	require.True(t, errors.Is(err, ErrInvalidType), err)
+}
+
+func TestDeserializeTooManyElements(t *testing.T) {
+	item := Make(0)
+	for i := 0; i < MaxDeserialized-1; i++ { // 1 for zero inner element.
+		item = Make([]Item{item})
+	}
+	data, err := Serialize(item)
+	require.NoError(t, err)
+	_, err = Deserialize(data)
+	require.NoError(t, err)
+
+	item = Make([]Item{item})
+	data, err = Serialize(item)
+	require.NoError(t, err)
+	_, err = Deserialize(data)
+	require.True(t, errors.Is(err, ErrTooBig), err)
+}
+
 func BenchmarkEncodeBinary(b *testing.B) {
 	arr := getBigArray(15)
 
diff --git a/pkg/vm/vm.go b/pkg/vm/vm.go
index 7ae6d5cdf..9d996d7f8 100644
--- a/pkg/vm/vm.go
+++ b/pkg/vm/vm.go
@@ -918,7 +918,7 @@ func (v *VM) execute(ctx *Context, op opcode.Opcode, parameter []byte) (err erro
 	case opcode.POW:
 		exp := v.estack.Pop().BigInt()
 		a := v.estack.Pop().BigInt()
-		if ei := exp.Int64(); !exp.IsInt64() || ei > math.MaxInt32 || ei < 0 {
+		if ei := exp.Uint64(); !exp.IsUint64() || ei > maxSHLArg {
 			panic("invalid exponent")
 		}
 		v.estack.PushVal(new(big.Int).Exp(a, exp, nil))
@@ -1027,47 +1027,37 @@ func (v *VM) execute(ctx *Context, op opcode.Opcode, parameter []byte) (err erro
 	case opcode.NEWARRAY0:
 		v.estack.PushVal(stackitem.NewArray([]stackitem.Item{}))
 
-	case opcode.NEWARRAY, opcode.NEWARRAYT:
-		item := v.estack.Pop()
-		n := item.BigInt().Int64()
-		if n > stackitem.MaxArraySize {
-			panic("too long array")
+	case opcode.NEWARRAY, opcode.NEWARRAYT, opcode.NEWSTRUCT:
+		n := toInt(v.estack.Pop().BigInt())
+		if n < 0 || n > MaxStackSize {
+			panic("wrong number of elements")
 		}
 		typ := stackitem.AnyT
 		if op == opcode.NEWARRAYT {
 			typ = stackitem.Type(parameter[0])
 		}
 		items := makeArrayOfType(int(n), typ)
-		v.estack.PushVal(stackitem.NewArray(items))
+		var res stackitem.Item
+		if op == opcode.NEWSTRUCT {
+			res = stackitem.NewStruct(items)
+		} else {
+			res = stackitem.NewArray(items)
+		}
+		v.estack.PushVal(res)
 
 	case opcode.NEWSTRUCT0:
 		v.estack.PushVal(stackitem.NewStruct([]stackitem.Item{}))
 
-	case opcode.NEWSTRUCT:
-		item := v.estack.Pop()
-		n := item.BigInt().Int64()
-		if n > stackitem.MaxArraySize {
-			panic("too long struct")
-		}
-		items := makeArrayOfType(int(n), stackitem.AnyT)
-		v.estack.PushVal(stackitem.NewStruct(items))
-
 	case opcode.APPEND:
 		itemElem := v.estack.Pop()
 		arrElem := v.estack.Pop()
 
-		val := cloneIfStruct(itemElem.value, MaxStackSize-v.refs.size)
+		val := cloneIfStruct(itemElem.value)
 
 		switch t := arrElem.value.(type) {
 		case *stackitem.Array:
-			if t.Len() >= stackitem.MaxArraySize {
-				panic("too long array")
-			}
 			t.Append(val)
 		case *stackitem.Struct:
-			if t.Len() >= stackitem.MaxArraySize {
-				panic("too long struct")
-			}
 			t.Append(val)
 		default:
 			panic("APPEND: not of underlying type Array")
@@ -1076,8 +1066,8 @@ func (v *VM) execute(ctx *Context, op opcode.Opcode, parameter []byte) (err erro
 		v.refs.Add(val)
 
 	case opcode.PACK:
-		n := int(v.estack.Pop().BigInt().Int64())
-		if n < 0 || n > v.estack.Len() || n > stackitem.MaxArraySize {
+		n := toInt(v.estack.Pop().BigInt())
+		if n < 0 || n > v.estack.Len() {
 			panic("OPACK: invalid length")
 		}
 
@@ -1148,8 +1138,6 @@ func (v *VM) execute(ctx *Context, op opcode.Opcode, parameter []byte) (err erro
 		case *stackitem.Map:
 			if i := t.Index(key.value); i >= 0 {
 				v.refs.Remove(t.Value().([]stackitem.MapElement)[i].Value)
-			} else if t.Len() >= stackitem.MaxArraySize {
-				panic("too big map")
 			}
 			t.Add(key.value, item)
 			v.refs.Add(item)
@@ -1370,12 +1358,12 @@ func (v *VM) execute(ctx *Context, op opcode.Opcode, parameter []byte) (err erro
 			src := t.Value().([]stackitem.Item)
 			arr = make([]stackitem.Item, len(src))
 			for i := range src {
-				arr[i] = cloneIfStruct(src[i], MaxStackSize-v.refs.size)
+				arr[i] = cloneIfStruct(src[i])
 			}
 		case *stackitem.Map:
 			arr = make([]stackitem.Item, 0, t.Len())
 			for k := range t.Value().([]stackitem.MapElement) {
-				arr = append(arr, cloneIfStruct(t.Value().([]stackitem.MapElement)[k].Value, MaxStackSize-v.refs.size))
+				arr = append(arr, cloneIfStruct(t.Value().([]stackitem.MapElement)[k].Value))
 			}
 		default:
 			panic("not a Map, Array or Struct")
@@ -1741,10 +1729,10 @@ func checkMultisig1(v *VM, curve elliptic.Curve, h []byte, pkeys [][]byte, sig [
 	return false
 }
 
-func cloneIfStruct(item stackitem.Item, limit int) stackitem.Item {
+func cloneIfStruct(item stackitem.Item) stackitem.Item {
 	switch it := item.(type) {
 	case *stackitem.Struct:
-		ret, err := it.Clone(limit)
+		ret, err := it.Clone()
 		if err != nil {
 			panic(err)
 		}
diff --git a/pkg/vm/vm_test.go b/pkg/vm/vm_test.go
index 484b3cda1..8fb07646f 100644
--- a/pkg/vm/vm_test.go
+++ b/pkg/vm/vm_test.go
@@ -6,7 +6,6 @@ import (
 	"encoding/hex"
 	"errors"
 	"fmt"
-	"math"
 	"math/big"
 	"math/rand"
 	"testing"
@@ -719,7 +718,7 @@ func TestPOW(t *testing.T) {
 	t.Run("good, negative, odd", getTestFuncForVM(prog, -8, -2, 3))
 	t.Run("zero", getTestFuncForVM(prog, 1, 3, 0))
 	t.Run("negative exponent", getTestFuncForVM(prog, nil, 3, -1))
-	t.Run("too big exponent", getTestFuncForVM(prog, nil, 1, math.MaxInt32+1))
+	t.Run("too big exponent", getTestFuncForVM(prog, nil, 1, maxSHLArg+1))
 }
 
 func TestSQRT(t *testing.T) {
@@ -1058,7 +1057,7 @@ func TestNEWSTRUCT0(t *testing.T) {
 func TestNEWARRAYArray(t *testing.T) {
 	prog := makeProgram(opcode.NEWARRAY)
 	t.Run("ByteArray", getTestFuncForVM(prog, stackitem.NewArray([]stackitem.Item{}), []byte{}))
-	t.Run("BadSize", getTestFuncForVM(prog, nil, stackitem.MaxArraySize+1))
+	t.Run("BadSize", getTestFuncForVM(prog, nil, MaxStackSize+1))
 	t.Run("Integer", getTestFuncForVM(prog, []stackitem.Item{stackitem.Null{}}, 1))
 }
 
@@ -1109,7 +1108,7 @@ func TestNEWARRAYT(t *testing.T) {
 func TestNEWSTRUCT(t *testing.T) {
 	prog := makeProgram(opcode.NEWSTRUCT)
 	t.Run("ByteArray", getTestFuncForVM(prog, stackitem.NewStruct([]stackitem.Item{}), []byte{}))
-	t.Run("BadSize", getTestFuncForVM(prog, nil, stackitem.MaxArraySize+1))
+	t.Run("BadSize", getTestFuncForVM(prog, nil, MaxStackSize+1))
 	t.Run("Integer", getTestFuncForVM(prog, stackitem.NewStruct([]stackitem.Item{stackitem.Null{}}), 1))
 }
 
@@ -1137,15 +1136,20 @@ func TestAPPENDBad(t *testing.T) {
 func TestAPPENDGoodSizeLimit(t *testing.T) {
 	prog := makeProgram(opcode.NEWARRAY, opcode.DUP, opcode.PUSH0, opcode.APPEND)
 	vm := load(prog)
-	vm.estack.PushVal(stackitem.MaxArraySize - 1)
+	vm.estack.PushVal(MaxStackSize - 3) // 1 for array, 1 for copy, 1 for pushed 0.
 	runVM(t, vm)
 	assert.Equal(t, 1, vm.estack.Len())
-	assert.Equal(t, stackitem.MaxArraySize, len(vm.estack.Pop().Array()))
+	assert.Equal(t, MaxStackSize-2, len(vm.estack.Pop().Array()))
 }
 
 func TestAPPENDBadSizeLimit(t *testing.T) {
 	prog := makeProgram(opcode.NEWARRAY, opcode.DUP, opcode.PUSH0, opcode.APPEND)
-	runWithArgs(t, prog, nil, stackitem.MaxArraySize)
+	runWithArgs(t, prog, nil, MaxStackSize)
+}
+
+func TestAPPENDRefSizeLimit(t *testing.T) {
+	prog := makeProgram(opcode.NEWARRAY0, opcode.DUP, opcode.DUP, opcode.APPEND, opcode.JMP, 0xfd)
+	runWithArgs(t, prog, nil)
 }
 
 func TestPICKITEM(t *testing.T) {
@@ -1206,19 +1210,19 @@ func TestSETITEMMap(t *testing.T) {
 func TestSETITEMBigMapBad(t *testing.T) {
 	prog := makeProgram(opcode.SETITEM)
 	m := stackitem.NewMap()
-	for i := 0; i < stackitem.MaxArraySize; i++ {
+	for i := 0; i < MaxStackSize; i++ {
 		m.Add(stackitem.Make(i), stackitem.Make(i))
 	}
 
-	runWithArgs(t, prog, nil, m, stackitem.MaxArraySize, 0)
+	runWithArgs(t, prog, nil, m, m, MaxStackSize, 0)
 }
 
 // This test checks is SETITEM properly updates reference counter.
-// 1. Create 2 arrays of size MaxArraySize - 3. (MaxStackSize = 2 * MaxArraySize)
+// 1. Create 2 arrays of size MaxStackSize/2 - 3.
 // 2. SETITEM each of them to a map.
 // 3. Replace each of them with a scalar value.
 func TestSETITEMMapStackLimit(t *testing.T) {
-	size := stackitem.MaxArraySize - 3
+	size := MaxStackSize/2 - 3
 	m := stackitem.NewMap()
 	m.Add(stackitem.NewBigInteger(big.NewInt(1)), stackitem.NewArray(makeArrayOfType(size, stackitem.BooleanT)))
 	m.Add(stackitem.NewBigInteger(big.NewInt(2)), stackitem.NewArray(makeArrayOfType(size, stackitem.BooleanT)))
@@ -1238,7 +1242,7 @@ func TestSETITEMBigMapGood(t *testing.T) {
 	vm := load(prog)
 
 	m := stackitem.NewMap()
-	for i := 0; i < stackitem.MaxArraySize; i++ {
+	for i := 0; i < MaxStackSize-3; i++ {
 		m.Add(stackitem.Make(i), stackitem.Make(i))
 	}
 	vm.estack.Push(&Element{value: m})
@@ -1724,16 +1728,6 @@ func TestPACK(t *testing.T) {
 	t.Run("Good0Len", getTestFuncForVM(prog, []stackitem.Item{}, 0))
 }
 
-func TestPACKBigLen(t *testing.T) {
-	prog := makeProgram(opcode.PACK)
-	vm := load(prog)
-	for i := 0; i <= stackitem.MaxArraySize; i++ {
-		vm.estack.PushVal(0)
-	}
-	vm.estack.PushVal(stackitem.MaxArraySize + 1)
-	checkVMFailed(t, vm)
-}
-
 func TestPACKGood(t *testing.T) {
 	prog := makeProgram(opcode.PACK)
 	elements := []int{55, 34, 42}
@@ -1757,7 +1751,7 @@ func TestPACKGood(t *testing.T) {
 
 func TestPACK_UNPACK_MaxSize(t *testing.T) {
 	prog := makeProgram(opcode.PACK, opcode.UNPACK)
-	elements := make([]int, stackitem.MaxArraySize)
+	elements := make([]int, MaxStackSize-2)
 	vm := load(prog)
 	// canary
 	vm.estack.PushVal(1)
@@ -1780,7 +1774,7 @@ func TestPACK_UNPACK_MaxSize(t *testing.T) {
 
 func TestPACK_UNPACK_PACK_MaxSize(t *testing.T) {
 	prog := makeProgram(opcode.PACK, opcode.UNPACK, opcode.PACK)
-	elements := make([]int, stackitem.MaxArraySize)
+	elements := make([]int, MaxStackSize-2)
 	vm := load(prog)
 	// canary
 	vm.estack.PushVal(1)
@@ -2451,6 +2445,14 @@ func TestNestedStructClone(t *testing.T) {
 	}
 }
 
+func TestNestedStructEquals(t *testing.T) {
+	h := "560112c501fe0160589d604a12c0db415824f7509d4a102aec4597" // See neo-project/neo-vm#426.
+	prog, err := hex.DecodeString(h)
+	require.NoError(t, err)
+	vm := load(prog)
+	checkVMFailed(t, vm)
+}
+
 func makeProgram(opcodes ...opcode.Opcode) []byte {
 	prog := make([]byte, len(opcodes)+1) // RET
 	for i := 0; i < len(opcodes); i++ {