diff --git a/metadata/metadata.go b/metadata/metadata.go
index 8b4ed9e1..e910f9a8 100644
--- a/metadata/metadata.go
+++ b/metadata/metadata.go
@@ -64,7 +64,7 @@ func encodeKeyValue(k, v string) (string, string) {
 	if isASCII(v) {
 		return k, v
 	}
-	key := k + binHdrSuffix
+	key := strings.ToLower(k + binHdrSuffix)
 	val := base64.StdEncoding.EncodeToString([]byte(v))
 	return key, string(val)
 }
@@ -85,14 +85,14 @@ 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 a MD from given key-value map.
 func New(m map[string]string) MD {
 	md := MD{}
 	for k, v := range m {
 		key, val := encodeKeyValue(k, v)
-		md[key] = val
+		md[key] = append(md[key],val)
 	}
 	return md
 }
@@ -111,7 +111,7 @@ func Pairs(kv ...string) MD {
 			continue
 		}
 		key, val := encodeKeyValue(k, s)
-		md[key] = val
+		md[key] = append(md[key],val)
 	}
 	return md
 }
@@ -125,7 +125,9 @@ func (md MD) Len() int {
 func (md MD) Copy() MD {
 	out := MD{}
 	for k, v := range md {
-		out[k] = v
+		for _, i := range v {
+			out[k] = append(out[k],i)
+		}
 	}
 	return out
 }
diff --git a/test/end2end_test.go b/test/end2end_test.go
index fb83b452..c23d8262 100644
--- a/test/end2end_test.go
+++ b/test/end2end_test.go
@@ -59,8 +59,8 @@ import (
 
 var (
 	testMetadata = metadata.MD{
-		"key1": "value1",
-		"key2": "value2",
+		"key1": []string{"value1"},
+		"key2": []string{"value2"},
 	}
 	testAppUA = "myApp1/1.0 myApp2/0.9"
 )
@@ -75,7 +75,12 @@ func (s *testServer) EmptyCall(ctx context.Context, in *testpb.Empty) (*testpb.E
 		if _, ok := md["user-agent"]; !ok {
 			return nil, grpc.Errorf(codes.DataLoss, "got extra metadata")
 		}
-		grpc.SendHeader(ctx, metadata.Pairs("ua", md["user-agent"]))
+	//	kv := []string{"ua"}
+	//	for _, entry := range md["user-agent"]{
+	//		kv = append(kv,entry)
+	//	}
+	//	grpc.SendHeader(ctx, metadata.Pairs(kv))
+	grpc.SendHeader(ctx, metadata.Pairs("ua", md["user-agent"][0]))
 	}
 	return new(testpb.Empty), nil
 }
@@ -499,7 +504,7 @@ func testEmptyUnaryWithUserAgent(t *testing.T, e env) {
 	if err != nil || !proto.Equal(&testpb.Empty{}, reply) {
 		t.Fatalf("TestService/EmptyCall(_, _) = %v, %v, want %v, <nil>", reply, err, &testpb.Empty{})
 	}
-	if v, ok := header["ua"]; !ok || v != testAppUA {
+	if v, ok := header["ua"]; !ok || v[0] != testAppUA {
 		t.Fatalf("header[\"ua\"] = %q, %t, want %q, true", v, ok, testAppUA)
 	}
 	tearDown(s, cc)
diff --git a/transport/http2_client.go b/transport/http2_client.go
index 0986ef01..02147e97 100644
--- a/transport/http2_client.go
+++ b/transport/http2_client.go
@@ -294,9 +294,12 @@ func (t *http2Client) NewStream(ctx context.Context, callHdr *CallHdr) (_ *Strea
 	if md, ok := metadata.FromContext(ctx); ok {
 		hasMD = true
 		for k, v := range md {
-			t.hEnc.WriteField(hpack.HeaderField{Name: k, Value: v})
+			for _, entry := range v {
+			t.hEnc.WriteField(hpack.HeaderField{Name: k, Value: entry})
 		}
 	}
+
+	}
 	first := true
 	// Sends the headers in a single batch even when they span multiple frames.
 	for !endHeaders {
diff --git a/transport/http2_server.go b/transport/http2_server.go
index 2ec2bb13..a8e78cdb 100644
--- a/transport/http2_server.go
+++ b/transport/http2_server.go
@@ -440,8 +440,11 @@ func (t *http2Server) WriteHeader(s *Stream, md metadata.MD) error {
 	t.hEnc.WriteField(hpack.HeaderField{Name: ":status", Value: "200"})
 	t.hEnc.WriteField(hpack.HeaderField{Name: "content-type", Value: "application/grpc"})
 	for k, v := range md {
-		t.hEnc.WriteField(hpack.HeaderField{Name: k, Value: v})
+		for _, entry := range v{
+		t.hEnc.WriteField(hpack.HeaderField{Name: k, Value: entry})
 	}
+}
+
 	if err := t.writeHeaders(s, t.hBuf, false); err != nil {
 		return err
 	}
@@ -473,8 +476,10 @@ func (t *http2Server) WriteStatus(s *Stream, statusCode codes.Code, statusDesc s
 	t.hEnc.WriteField(hpack.HeaderField{Name: "grpc-message", Value: statusDesc})
 	// Attach the trailer metadata.
 	for k, v := range s.trailer {
-		t.hEnc.WriteField(hpack.HeaderField{Name: k, Value: v})
+		for _, entry := range v {
+		t.hEnc.WriteField(hpack.HeaderField{Name: k, Value: entry})
 	}
+}
 	if err := t.writeHeaders(s, t.hBuf, true); err != nil {
 		t.Close()
 		return err
diff --git a/transport/http_util.go b/transport/http_util.go
index af84fbf6..6cc8d335 100644
--- a/transport/http_util.go
+++ b/transport/http_util.go
@@ -100,7 +100,7 @@ type decodeState struct {
 	timeout    time.Duration
 	method     string
 	// key-value metadata map from the peer.
-	mdata map[string]string
+	mdata map[string][]string
 }
 
 // An hpackDecoder decodes HTTP2 headers which may span multiple frames.
@@ -173,14 +173,14 @@ func newHPACKDecoder() *hpackDecoder {
 					f.Value = f.Value[:i]
 				}
 				if d.state.mdata == nil {
-					d.state.mdata = make(map[string]string)
+					d.state.mdata = make(map[string][]string)
 				}
 				k, v, err := metadata.DecodeKeyValue(f.Name, f.Value)
 				if err != nil {
 					grpclog.Printf("Failed to decode (%q, %q): %v", f.Name, f.Value, err)
 					return
 				}
-				d.state.mdata[k] = v
+				d.state.mdata[k]= append(d.state.mdata[k],v)
 			}
 		}
 	})