diff --git a/bind/objc/SeqTest.m b/bind/objc/SeqTest.m
index 6c64bb2..d814ee2 100644
--- a/bind/objc/SeqTest.m
+++ b/bind/objc/SeqTest.m
@@ -27,6 +27,18 @@ void testHello(NSString *input) {
   }
 }
 
+void testBytesAppend(NSString *a, NSString *b) {
+  NSData *data_a = [a dataUsingEncoding:NSUTF8StringEncoding];
+  NSData *data_b = [b dataUsingEncoding:NSUTF8StringEncoding];
+  NSData *gotData = GoTestpkg_BytesAppend(data_a, data_b);
+  NSString *got =
+      [[NSString alloc] initWithData:gotData encoding:NSUTF8StringEncoding];
+  NSString *want = [a stringByAppendingString:b];
+  if (![got isEqualToString:want]) {
+    ERROR(@"want %@\nGoTestpkg_BytesAppend(%@, %@) = %@", want, a, b, got);
+  }
+}
+
 // Invokes functions and object methods defined in Testpkg.h.
 //
 // TODO(hyangah): apply testing framework (e.g. XCTestCase)
@@ -48,6 +60,8 @@ int main(void) {
         0xD83D, 0xDCA9,
     }; // utf-16, pile of poo.
     testHello([NSString stringWithCharacters:t length:2]);
+
+    testBytesAppend(@"Foo", @"Bar");
   }
 
   fprintf(stderr, "%s\n", err ? "FAIL" : "PASS");
diff --git a/bind/objc/seq.h b/bind/objc/seq.h
index d6cb474..27ec9d3 100644
--- a/bind/objc/seq.h
+++ b/bind/objc/seq.h
@@ -22,6 +22,7 @@ extern int64_t go_seq_readInt64(GoSeq *seq);
 extern float go_seq_readFloat32(GoSeq *seq);
 extern double go_seq_readFloat64(GoSeq *seq);
 extern NSString *go_seq_readUTF8(GoSeq *seq);
+extern NSData *go_seq_readByteArray(GoSeq *seq);
 
 extern void go_seq_writeInt8(GoSeq *seq, int8_t v);
 extern void go_seq_writeInt16(GoSeq *seq, int16_t v);
@@ -31,6 +32,10 @@ extern void go_seq_writeFloat32(GoSeq *seq, float v);
 extern void go_seq_writeFloat64(GoSeq *seq, double v);
 extern void go_seq_writeUTF8(GoSeq *seq, NSString *v);
 
+// go_seq_writeByteArray writes the data bytes to the seq. Note that the
+// data should be valid until the the subsequent go_seq_send call completes.
+extern void go_seq_writeByteArray(GoSeq *seq, NSData *data);
+
 // go_seq_send sends a function invocation request to Go.
 // It blocks until the function completes.
 // If the request is for a method, the first element in req is
diff --git a/bind/objc/seq_darwin.m b/bind/objc/seq_darwin.m
index 9e6ad87..35b081d 100644
--- a/bind/objc/seq_darwin.m
+++ b/bind/objc/seq_darwin.m
@@ -191,6 +191,28 @@ void go_seq_writeUTF8(GoSeq *seq, NSString *s) {
   return;
 }
 
+NSData *go_seq_readByteArray(GoSeq *seq) {
+  int64_t sz = *MEM_READ(seq, int64_t);
+  if (sz == 0) {
+    return [NSData data];
+  }
+  // BUG(hyangah): it is possible that *ptr is already GC'd by Go runtime.
+  void *ptr = (void *)(*MEM_READ(seq, int64_t));
+  return [NSData dataWithBytes:ptr length:sz];
+}
+
+void go_seq_writeByteArray(GoSeq *seq, NSData *data) {
+  int64_t sz = data.length;
+  MEM_WRITE(seq, int64_t) = sz;
+  if (sz == 0) {
+    return;
+  }
+
+  int64_t ptr = data.bytes;
+  MEM_WRITE(seq, int64_t) = ptr;
+  return;
+}
+
 void go_seq_send(char *descriptor, int code, GoSeq *req_seq, GoSeq *res_seq) {
   if (descriptor == NULL) {
     LOG_FATAL(@"invalid NULL descriptor");
diff --git a/bind/objc/testpkg/go_testpkg/go_testpkg.go b/bind/objc/testpkg/go_testpkg/go_testpkg.go
index 887362d..d70ad82 100644
--- a/bind/objc/testpkg/go_testpkg/go_testpkg.go
+++ b/bind/objc/testpkg/go_testpkg/go_testpkg.go
@@ -13,6 +13,13 @@ import (
 	"golang.org/x/mobile/bind/seq"
 )
 
+func proxy_BytesAppend(out, in *seq.Buffer) {
+	param_a := in.ReadByteArray()
+	param_b := in.ReadByteArray()
+	res := testpkg.BytesAppend(param_a, param_b)
+	out.WriteByteArray(res)
+}
+
 func proxy_Hello(out, in *seq.Buffer) {
 	param_s := in.ReadString()
 	res := testpkg.Hello(param_s)
@@ -36,8 +43,9 @@ func proxy_Sum(out, in *seq.Buffer) {
 }
 
 func init() {
-	seq.Register("testpkg", 1, proxy_Hello)
-	seq.Register("testpkg", 2, proxy_Hi)
-	seq.Register("testpkg", 3, proxy_Int)
-	seq.Register("testpkg", 4, proxy_Sum)
+	seq.Register("testpkg", 1, proxy_BytesAppend)
+	seq.Register("testpkg", 2, proxy_Hello)
+	seq.Register("testpkg", 3, proxy_Hi)
+	seq.Register("testpkg", 4, proxy_Int)
+	seq.Register("testpkg", 5, proxy_Sum)
 }
diff --git a/bind/objc/testpkg/objc_testpkg/GoTestpkg.h b/bind/objc/testpkg/objc_testpkg/GoTestpkg.h
index a5bf2e6..45d1eaa 100644
--- a/bind/objc/testpkg/objc_testpkg/GoTestpkg.h
+++ b/bind/objc/testpkg/objc_testpkg/GoTestpkg.h
@@ -9,6 +9,7 @@
 
 #include "seq.h"
 
+FOUNDATION_EXPORT NSData *GoTestpkg_BytesAppend(NSData *a, NSData *b);
 FOUNDATION_EXPORT void GoTestpkg_Hi();
 FOUNDATION_EXPORT void GoTestpkg_Int(int32_t x);
 FOUNDATION_EXPORT int64_t GoTestpkg_Sum(int64_t x, int64_t y);
diff --git a/bind/objc/testpkg/objc_testpkg/GoTestpkg.m b/bind/objc/testpkg/objc_testpkg/GoTestpkg.m
index 6d7bff7..b92f946 100644
--- a/bind/objc/testpkg/objc_testpkg/GoTestpkg.m
+++ b/bind/objc/testpkg/objc_testpkg/GoTestpkg.m
@@ -11,10 +11,11 @@
 
 #define _DESCRIPTOR_ "testpkg"
 
-#define _CALL_Hello_ 1
-#define _CALL_Hi_ 2
-#define _CALL_Int_ 3
-#define _CALL_Sum_ 4
+#define _CALL_BytesAppend_ 1
+#define _CALL_Hello_ 2
+#define _CALL_Hi_ 3
+#define _CALL_Int_ 4
+#define _CALL_Sum_ 5
 
 #define INIT_SEQ(X)                                                            \
   GoSeq X;                                                                     \
@@ -22,6 +23,19 @@
 
 #define FREE_SEQ(X) go_seq_free(&X);
 
+NSData *GoTestpkg_BytesAppend(NSData *a, NSData *b) {
+  INIT_SEQ(in);
+  INIT_SEQ(out);
+  go_seq_writeByteArray(&in, a);
+  go_seq_writeByteArray(&in, b);
+  go_seq_send(_DESCRIPTOR_, _CALL_BytesAppend_, &in, &out);
+
+  NSData *ret = go_seq_readByteArray(&out);
+  FREE_SEQ(out);
+  FREE_SEQ(in);
+  return ret;
+}
+
 void GoTestpkg_Hi() {
   // No input, output.
   go_seq_send(_DESCRIPTOR_, _CALL_Hi_, NULL, NULL);
diff --git a/bind/objc/testpkg/testpkg.go b/bind/objc/testpkg/testpkg.go
index 43df6e9..9750003 100644
--- a/bind/objc/testpkg/testpkg.go
+++ b/bind/objc/testpkg/testpkg.go
@@ -23,3 +23,7 @@ func Sum(x, y int64) int64 {
 func Hello(s string) string {
 	return fmt.Sprintf("Hello, %s!", s)
 }
+
+func BytesAppend(a []byte, b []byte) []byte {
+	return append(a, b...)
+}