diff --git a/pkg/vm/context.go b/pkg/vm/context.go
index 462531711..cb540cea2 100644
--- a/pkg/vm/context.go
+++ b/pkg/vm/context.go
@@ -172,7 +172,10 @@ func (c *Context) Dup() StackItem {
 
 // ToContractParameter implements StackItem interface.
 func (c *Context) ToContractParameter(map[StackItem]bool) smartcontract.Parameter {
-	panic("Not implemented")
+	return smartcontract.Parameter{
+		Type:  smartcontract.StringType,
+		Value: c.String(),
+	}
 }
 
 func (c *Context) atBreakPoint() bool {
diff --git a/pkg/vm/output.go b/pkg/vm/output.go
deleted file mode 100644
index 46c27d3f9..000000000
--- a/pkg/vm/output.go
+++ /dev/null
@@ -1,47 +0,0 @@
-package vm
-
-import "encoding/json"
-
-// StackOutput holds information about the stack, used for pretty printing
-// the stack.
-type stackItem struct {
-	Value interface{} `json:"value"`
-	Type  string      `json:"type"`
-}
-
-func appendToItems(items *[]stackItem, val StackItem, seen map[StackItem]bool) {
-	if arr, ok := val.Value().([]StackItem); ok {
-		if seen[val] {
-			return
-		}
-		seen[val] = true
-		intItems := make([]stackItem, 0, len(arr))
-		for _, v := range arr {
-			appendToItems(&intItems, v, seen)
-		}
-		*items = append(*items, stackItem{
-			Value: intItems,
-			Type:  val.String(),
-		})
-
-	} else {
-		*items = append(*items, stackItem{
-			Value: val,
-			Type:  val.String(),
-		})
-	}
-}
-
-func stackToArray(s *Stack) []stackItem {
-	items := make([]stackItem, 0, s.Len())
-	seen := make(map[StackItem]bool)
-	s.IterBack(func(e *Element) {
-		appendToItems(&items, e.value, seen)
-	})
-	return items
-}
-
-func buildStackOutput(s *Stack) string {
-	b, _ := json.MarshalIndent(stackToArray(s), "", "    ")
-	return string(b)
-}
diff --git a/pkg/vm/stack.go b/pkg/vm/stack.go
index b968d9cc2..bc3142363 100644
--- a/pkg/vm/stack.go
+++ b/pkg/vm/stack.go
@@ -6,6 +6,7 @@ import (
 	"fmt"
 	"math/big"
 
+	"github.com/CityOfZion/neo-go/pkg/smartcontract"
 	"github.com/CityOfZion/neo-go/pkg/vm/emit"
 )
 
@@ -469,7 +470,18 @@ func (s *Stack) popSigElements() ([][]byte, error) {
 	return elems, nil
 }
 
+// ToContractParameters converts Stack to slice of smartcontract.Parameter.
+func (s *Stack) ToContractParameters() []smartcontract.Parameter {
+	items := make([]smartcontract.Parameter, 0, s.Len())
+	s.IterBack(func(e *Element) {
+		// Each item is independent.
+		seen := make(map[StackItem]bool)
+		items = append(items, e.value.ToContractParameter(seen))
+	})
+	return items
+}
+
 // MarshalJSON implements JSON marshalling interface.
 func (s *Stack) MarshalJSON() ([]byte, error) {
-	return json.Marshal(stackToArray(s))
+	return json.Marshal(s.ToContractParameters())
 }
diff --git a/pkg/vm/vm.go b/pkg/vm/vm.go
index b08795ef7..e5300377b 100644
--- a/pkg/vm/vm.go
+++ b/pkg/vm/vm.go
@@ -3,6 +3,7 @@ package vm
 import (
 	"crypto/sha1"
 	"encoding/binary"
+	"encoding/json"
 	"fmt"
 	"io/ioutil"
 	"math/big"
@@ -301,7 +302,8 @@ func (v *VM) Stack(n string) string {
 	if n == "estack" {
 		s = v.estack
 	}
-	return buildStackOutput(s)
+	b, _ := json.MarshalIndent(s.ToContractParameters(), "", "    ")
+	return string(b)
 }
 
 // State returns string representation of the state for the VM.