diff --git a/httpx/_content.py b/httpx/_content.py
index 6f479a0885..f4acfc4045 100644
--- a/httpx/_content.py
+++ b/httpx/_content.py
@@ -61,7 +61,11 @@ def __iter__(self) -> Iterator[bytes]:
         else:
             # Otherwise iterate.
             for part in self._stream:
-                yield part
+                # For bytes types, should use yield to send data in
+                # chunks. Sending a very large part at once will
+                # result in extremely slow transmission.
+                for i in range(0, len(part), self.CHUNK_SIZE):
+                    yield part[i : i + self.CHUNK_SIZE]
 
 
 class AsyncIteratorByteStream(AsyncByteStream):