diff --git a/google/api_core/bidi.py b/google/api_core/bidi.py
index be52d97d..db19f286 100644
--- a/google/api_core/bidi.py
+++ b/google/api_core/bidi.py
@@ -240,7 +240,8 @@ class BidiRpc(object):
             yield. This is useful if an initial request is needed to start the
             stream.
         metadata (Sequence[Tuple(str, str)]): RPC metadata to include in
-            the request.
+            the request. If no metadata is provided, metadata from
+            start_rpc will be used.
     """
 
     def __init__(self, start_rpc, initial_request=None, metadata=None):
@@ -277,7 +278,11 @@ def open(self):
         request_generator = _RequestQueueGenerator(
             self._request_queue, initial_request=self._initial_request
         )
-        call = self._start_rpc(iter(request_generator), metadata=self._rpc_metadata)
+        if self._rpc_metadata:
+            call = self._start_rpc(iter(request_generator), metadata=self._rpc_metadata)
+        # use metadata from self._start_rpc if no other metadata is specified
+        else:
+            call = self._start_rpc(iter(request_generator))
 
         request_generator.call = call
 
diff --git a/tests/unit/test_bidi.py b/tests/unit/test_bidi.py
index 52215cbd..24a8ff0d 100644
--- a/tests/unit/test_bidi.py
+++ b/tests/unit/test_bidi.py
@@ -202,12 +202,12 @@ class _CallAndFuture(grpc.Call, grpc.Future):
     pass
 
 
-def make_rpc():
+def make_rpc(metadata=None):
     """Makes a mock RPC used to test Bidi classes."""
     call = mock.create_autospec(_CallAndFuture, instance=True)
     rpc = mock.create_autospec(grpc.StreamStreamMultiCallable, instance=True)
 
-    def rpc_side_effect(request, metadata=None):
+    def rpc_side_effect(request, metadata=metadata):
         call.is_active.return_value = True
         call.request = request
         call.metadata = metadata
@@ -265,12 +265,13 @@ def test_metadata(self):
         assert bidi_rpc.call.metadata == mock.sentinel.A
 
     def test_open(self):
-        rpc, call = make_rpc()
-        bidi_rpc = bidi.BidiRpc(rpc)
+        rpc, call = make_rpc(metadata=[(1, 2)])
+        bidi_rpc = bidi.BidiRpc(rpc, metadata=[(3, 4)])
 
         bidi_rpc.open()
 
         assert bidi_rpc.call == call
+        assert bidi_rpc.call.metadata == [(3, 4)]
         assert bidi_rpc.is_active
         call.add_done_callback.assert_called_once_with(bidi_rpc._on_call_done)
 
@@ -283,6 +284,14 @@ def test_open_error_already_open(self):
         with pytest.raises(ValueError):
             bidi_rpc.open()
 
+    def test_open_use_start_rpc_metadata(self):
+        rpc, _ = make_rpc(metadata=[(1, 2)])
+        bidi_rpc = bidi.BidiRpc(rpc)
+
+        bidi_rpc.open()
+
+        assert bidi_rpc.call.metadata == [(1, 2)]
+
     def test_close(self):
         rpc, call = make_rpc()
         bidi_rpc = bidi.BidiRpc(rpc)