diff --git a/starlette/testclient.py b/starlette/testclient.py
index 08d03fa5c..b9d5485c0 100644
--- a/starlette/testclient.py
+++ b/starlette/testclient.py
@@ -400,7 +400,6 @@ def receive_json(self, mode: str = "text") -> typing.Any:
 class TestClient(requests.Session):
     __test__ = False  # For pytest to not discover this up.
     task: "Future[None]"
-    portal: typing.Optional[anyio.abc.BlockingPortal] = None
 
     def __init__(
         self,
@@ -410,6 +409,7 @@ def __init__(
         root_path: str = "",
         backend: str = "asyncio",
         backend_options: typing.Optional[typing.Dict[str, typing.Any]] = None,
+        portal: typing.Optional[anyio.abc.BlockingPortal] = None,
     ) -> None:
         super().__init__()
         self.async_backend = _AsyncBackend(
@@ -434,6 +434,7 @@ def __init__(
         self.headers.update({"user-agent": "testclient"})
         self.app = asgi_app
         self.base_url = base_url
+        self.portal = portal
 
     @contextlib.contextmanager
     def _portal_factory(
@@ -506,13 +507,16 @@ def websocket_connect(
 
     def __enter__(self) -> "TestClient":
         with contextlib.ExitStack() as stack:
-            self.portal = portal = stack.enter_context(
-                anyio.start_blocking_portal(**self.async_backend)
-            )
+            if self.portal:
+                portal = self.portal
+            else:
+                portal = self.portal = stack.enter_context(
+                    anyio.start_blocking_portal(**self.async_backend)
+                )
 
-            @stack.callback
-            def reset_portal() -> None:
-                self.portal = None
+                @stack.callback
+                def reset_portal() -> None:
+                    self.portal = None
 
             self.stream_send = StapledObjectStream(
                 *anyio.create_memory_object_stream(math.inf)
diff --git a/tests/test_testclient.py b/tests/test_testclient.py
index 8c0666789..055749191 100644
--- a/tests/test_testclient.py
+++ b/tests/test_testclient.py
@@ -71,6 +71,31 @@ def homepage(request):
     assert response.json() == {"mock": "example"}
 
 
+def test_use_multiple_testclients_with_asyncio(test_client_factory, anyio_backend_name):
+    if anyio_backend_name != "asyncio":
+        return
+    service = Starlette()
+
+    @service.on_event("startup")
+    async def save_event_loop():
+        service.state.event_loop = asyncio.get_running_loop()
+
+    @service.route("/")
+    async def handle_request(request):
+        await service.state.event_loop.create_task(asyncio.sleep(0))
+        return JSONResponse({})
+
+    with test_client_factory(service) as parent_client:
+        client_2 = test_client_factory(service, portal=parent_client.portal)
+        assert client_2.get("/").json() == {}
+        assert parent_client.get("/").json() == {}
+
+        client_3 = test_client_factory(service, portal=parent_client.portal)
+        with client_3:
+            assert client_3.get("/").json() == {}
+            assert parent_client.get("/").json() == {}
+
+
 def test_use_testclient_as_contextmanager(test_client_factory, anyio_backend_name):
     """
     This test asserts a number of properties that are important for an