diff --git a/metadata/metadata_grpc.go b/metadata/metadata_grpc.go
index 8c880925..4c5102d3 100644
--- a/metadata/metadata_grpc.go
+++ b/metadata/metadata_grpc.go
@@ -1,6 +1,6 @@
 //go:build exclude
 
-//TODO need compare with micro metadata
+// TODO need compare with micro metadata
 package metadata
 
 import (
@@ -18,7 +18,7 @@ func DecodeKeyValue(k, v string) (string, string, error) {
 
 // MD is a mapping from metadata keys to values. Users should use the following
 // two convenience functions New and Pairs to generate MD.
-type MD map[string][]string
+type MD map[string]string
 
 // New creates an MD from a given key-value map.
 //
@@ -36,7 +36,7 @@ func New(m map[string]string) MD {
 	md := make(MD, len(m))
 	for k, val := range m {
 		key := strings.ToLower(k)
-		md[key] = append(md[key], val)
+		md[key] = val
 	}
 	return md
 }
@@ -61,7 +61,7 @@ func Pairs(kv ...string) MD {
 	md := make(MD, len(kv)/2)
 	for i := 0; i < len(kv); i += 2 {
 		key := strings.ToLower(kv[i])
-		md[key] = append(md[key], kv[i+1])
+		md[key] = kv[i+1]
 	}
 	return md
 }
@@ -75,7 +75,7 @@ func (md MD) Len() int {
 func (md MD) Copy() MD {
 	out := make(MD, len(md))
 	for k, v := range md {
-		out[k] = copyOf(v)
+		out[k] = v
 	}
 	return out
 }
@@ -83,7 +83,7 @@ func (md MD) Copy() MD {
 // Get obtains the values for a given key.
 //
 // k is converted to lowercase before searching in md.
-func (md MD) Get(k string) []string {
+func (md MD) Get(k string) string {
 	k = strings.ToLower(k)
 	return md[k]
 }
@@ -91,7 +91,7 @@ func (md MD) Get(k string) []string {
 // Set sets the value of a given key with a slice of values.
 //
 // k is converted to lowercase before storing in md.
-func (md MD) Set(k string, vals ...string) {
+func (md MD) Set(k string, vals string) {
 	if len(vals) == 0 {
 		return
 	}
@@ -103,12 +103,12 @@ func (md MD) Set(k string, vals ...string) {
 // that key.
 //
 // k is converted to lowercase before storing in md.
-func (md MD) Append(k string, vals ...string) {
+func (md MD) Append(k string, vals string) {
 	if len(vals) == 0 {
 		return
 	}
 	k = strings.ToLower(k)
-	md[k] = append(md[k], vals...)
+	md[k] = vals
 }
 
 // Delete removes the values for a given key k which is converted to lowercase
@@ -126,7 +126,7 @@ func Join(mds ...MD) MD {
 	out := MD{}
 	for _, md := range mds {
 		for k, v := range md {
-			out[k] = append(out[k], v...)
+			out[k] = v
 		}
 	}
 	return out
@@ -157,14 +157,13 @@ func AppendToOutgoingContext(ctx context.Context, kv ...string) context.Context
 		panic(fmt.Sprintf("metadata: AppendToOutgoingContext got an odd number of input pairs for metadata: %d", len(kv)))
 	}
 	md, _ := ctx.Value(mdOutgoingKey{}).(rawMD)
-	added := make([][]string, len(md.added)+1)
-	copy(added, md.added)
+
 	kvCopy := make([]string, 0, len(kv))
 	for i := 0; i < len(kv); i += 2 {
 		kvCopy = append(kvCopy, strings.ToLower(kv[i]), kv[i+1])
 	}
-	added[len(added)-1] = kvCopy
-	return context.WithValue(ctx, mdOutgoingKey{}, rawMD{md: md.md, added: added})
+
+	return context.WithValue(ctx, mdOutgoingKey{}, rawMD{md: md.md})
 }
 
 // FromIncomingContext returns the incoming metadata in ctx if it exists.
@@ -181,53 +180,24 @@ func FromIncomingContext(ctx context.Context) (MD, bool) {
 		// map, and there's no guarantee that the MD attached to the context is
 		// created using our helper functions.
 		key := strings.ToLower(k)
-		out[key] = copyOf(v)
+		out[key] = v
 	}
 	return out, true
 }
 
-// ValueFromIncomingContext returns the metadata value corresponding to the metadata
-// key from the incoming metadata if it exists. Keys are matched in a case insensitive
-// manner.
-func ValueFromIncomingContext(ctx context.Context, key string) []string {
-	md, ok := ctx.Value(mdIncomingKey{}).(MD)
-	if !ok {
-		return nil
-	}
-
-	if v, ok := md[key]; ok {
-		return copyOf(v)
-	}
-	for k, v := range md {
-		// Case insensitive comparison: MD is a map, and there's no guarantee
-		// that the MD attached to the context is created using our helper
-		// functions.
-		if strings.EqualFold(k, key) {
-			return copyOf(v)
-		}
-	}
-	return nil
-}
-
-func copyOf(v []string) []string {
-	vals := make([]string, len(v))
-	copy(vals, v)
-	return vals
-}
-
 // fromOutgoingContextRaw returns the un-merged, intermediary contents of rawMD.
 //
 // Remember to perform strings.ToLower on the keys, for both the returned MD (MD
 // is a map, there's no guarantee it's created using our helper functions) and
 // the extra kv pairs (AppendToOutgoingContext doesn't turn them into
 // lowercase).
-func fromOutgoingContextRaw(ctx context.Context) (MD, [][]string, bool) {
+func fromOutgoingContextRaw(ctx context.Context) (MD, bool) {
 	raw, ok := ctx.Value(mdOutgoingKey{}).(rawMD)
 	if !ok {
-		return nil, nil, false
+		return nil, false
 	}
 
-	return raw.md, raw.added, true
+	return raw.md, true
 }
 
 // FromOutgoingContext returns the outgoing metadata in ctx if it exists.
@@ -239,33 +209,18 @@ func FromOutgoingContext(ctx context.Context) (MD, bool) {
 		return nil, false
 	}
 
-	mdSize := len(raw.md)
-	for i := range raw.added {
-		mdSize += len(raw.added[i]) / 2
-	}
-
-	out := make(MD, mdSize)
+	out := make(MD, len(raw.md))
 	for k, v := range raw.md {
 		// We need to manually convert all keys to lower case, because MD is a
 		// map, and there's no guarantee that the MD attached to the context is
 		// created using our helper functions.
 		key := strings.ToLower(k)
-		out[key] = copyOf(v)
+		out[key] = v
 	}
-	for _, added := range raw.added {
-		if len(added)%2 == 1 {
-			panic(fmt.Sprintf("metadata: FromOutgoingContext got an odd number of input pairs for metadata: %d", len(added)))
-		}
 
-		for i := 0; i < len(added); i += 2 {
-			key := strings.ToLower(added[i])
-			out[key] = append(out[key], added[i+1])
-		}
-	}
 	return out, ok
 }
 
 type rawMD struct {
-	md    MD
-	added [][]string
+	md MD
 }