diff --git a/lib/includes/spdylay/spdylay.h b/lib/includes/spdylay/spdylay.h
index 6a083c8..a93df93 100644
--- a/lib/includes/spdylay/spdylay.h
+++ b/lib/includes/spdylay/spdylay.h
@@ -318,10 +318,24 @@ int spdylay_session_want_write(spdylay_session *session);
  *
  * This function creates copies of all name/value pairs in |nv|.
  *
+ * If |data_prd| is not NULL, it provides data which will be sent in
+ * subsequent DATA frames. In this case, "POST" must be specified with
+ * "method" key in |nv|. If |data_prd| is NULL, SYN_STREAM have
+ * FLAG_FIN.
+ *
  * This function returns 0 if it succeeds, or negative error code.
  */
 int spdylay_submit_request(spdylay_session *session, uint8_t pri,
-                           const char **nv);
+                           const char **nv,
+                           spdylay_data_provider *data_prd);
+
+/*
+ * Submits DATA frame to stream |stream_id|.
+ *
+ * This function returns 0 if it succeeds, or negative error code.
+ */
+int spdylay_submit_data(spdylay_session *session, int32_t stream_id,
+                        spdylay_data_provider *data_prd);
 
 /*
  * Submits SYN_REPLY frame against stream |stream_id|. |nv| must
diff --git a/lib/spdylay_session.c b/lib/spdylay_session.c
index 8ddf03a..c16b0c1 100644
--- a/lib/spdylay_session.c
+++ b/lib/spdylay_session.c
@@ -158,6 +158,7 @@ static void spdylay_outbound_item_free(spdylay_outbound_item *item)
     break;
   }
   free(item->frame);
+  free(item->aux_data);
 }
 
 void spdylay_session_del(spdylay_session *session)
@@ -180,7 +181,8 @@ void spdylay_session_del(spdylay_session *session)
 
 int spdylay_session_add_frame(spdylay_session *session,
                               spdylay_frame_type frame_type,
-                              spdylay_frame *frame)
+                              spdylay_frame *frame,
+                              void *aux_data)
 {
   int r;
   spdylay_outbound_item *item;
@@ -190,6 +192,7 @@ int spdylay_session_add_frame(spdylay_session *session,
   }
   item->frame_type = frame_type;
   item->frame = frame;
+  item->aux_data = aux_data;
   /* Set priority lowest at the moment. */
   item->pri = 3;
   switch(frame_type) {
@@ -255,7 +258,7 @@ int spdylay_session_add_rst_stream(spdylay_session *session,
     return SPDYLAY_ERR_NOMEM;
   }
   spdylay_frame_rst_stream_init(&frame->rst_stream, stream_id, status_code);
-  r = spdylay_session_add_frame(session, SPDYLAY_RST_STREAM, frame);
+  r = spdylay_session_add_frame(session, SPDYLAY_RST_STREAM, frame, NULL);
   if(r != 0) {
     spdylay_frame_rst_stream_free(&frame->rst_stream);
     free(frame);
@@ -349,12 +352,14 @@ ssize_t spdylay_session_prep_frame(spdylay_session *session,
   ssize_t framebuflen;
   switch(item->frame_type) {
   case SPDYLAY_SYN_STREAM: {
+    uint32_t stream_id;
     if(session->goaway_flags) {
       /* When GOAWAY is sent or received, peer must not send new
          SYN_STREAM. */
       return SPDYLAY_ERR_INVALID_FRAME;
     }
-    item->frame->syn_stream.stream_id = session->next_stream_id;
+    stream_id = session->next_stream_id;
+    item->frame->syn_stream.stream_id = stream_id;
     session->next_stream_id += 2;
     framebuflen = spdylay_frame_pack_syn_stream(&framebuf,
                                                 &item->frame->syn_stream,
@@ -362,13 +367,24 @@ ssize_t spdylay_session_prep_frame(spdylay_session *session,
     if(framebuflen < 0) {
       return framebuflen;
     }
-    if(spdylay_session_open_stream(session, item->frame->syn_stream.stream_id,
+    if(spdylay_session_open_stream(session, stream_id,
                                    item->frame->syn_stream.hd.flags,
                                    item->frame->syn_stream.pri,
                                    SPDYLAY_STREAM_INITIAL) == NULL) {
       free(framebuf);
       return SPDYLAY_ERR_NOMEM;
     }
+    if(item->aux_data) {
+      /* We assume aux_data is a pointer to spdylay_data_provider */
+      spdylay_data_provider *data_prd = (spdylay_data_provider*)item->aux_data;
+      int r;
+      r = spdylay_submit_data(session, stream_id, data_prd);
+      if(r != 0) {
+        free(framebuf);
+        spdylay_session_close_stream(session, stream_id);
+        return r;
+      }
+    }
     break;
   }
   case SPDYLAY_SYN_REPLY: {
@@ -1188,7 +1204,7 @@ int spdylay_session_add_ping(spdylay_session *session, uint32_t unique_id)
     return SPDYLAY_ERR_NOMEM;
   }
   spdylay_frame_ping_init(&frame->ping, unique_id);
-  r = spdylay_session_add_frame(session, SPDYLAY_PING, frame);
+  r = spdylay_session_add_frame(session, SPDYLAY_PING, frame, NULL);
   if(r != 0) {
     spdylay_frame_ping_free(&frame->ping);
     free(frame);
@@ -1206,7 +1222,7 @@ int spdylay_session_add_goaway(spdylay_session *session,
     return SPDYLAY_ERR_NOMEM;
   }
   spdylay_frame_goaway_init(&frame->goaway, last_good_stream_id);
-  r = spdylay_session_add_frame(session, SPDYLAY_GOAWAY, frame);
+  r = spdylay_session_add_frame(session, SPDYLAY_GOAWAY, frame, NULL);
   if(r != 0) {
     spdylay_frame_goaway_free(&frame->goaway);
     free(frame);
@@ -1248,60 +1264,76 @@ int spdylay_submit_response(spdylay_session *session,
   }
   spdylay_frame_syn_reply_init(&frame->syn_reply, flags, stream_id,
                                nv_copy);
-  r = spdylay_session_add_frame(session, SPDYLAY_SYN_REPLY, frame);
+  r = spdylay_session_add_frame(session, SPDYLAY_SYN_REPLY, frame, NULL);
   if(r != 0) {
     spdylay_frame_syn_reply_free(&frame->syn_reply);
     free(frame);
     return r;
   }
   if(data_prd != NULL) {
-    spdylay_frame *data_frame;
+    r = spdylay_submit_data(session, stream_id, data_prd);
     /* TODO If error is not FATAL, we should add RST_STREAM frame to
        cancel this stream. */
-    data_frame = malloc(sizeof(spdylay_frame));
-    if(data_frame == NULL) {
-      return SPDYLAY_ERR_NOMEM;
-    }
-    spdylay_frame_data_init(&data_frame->data, stream_id, data_prd);
-    r = spdylay_session_add_frame(session, SPDYLAY_DATA, data_frame);
-    if(r != 0) {
-      spdylay_frame_data_free(&data_frame->data);
-      free(data_frame);
-      return r;
-    }
   }
-  return 0;
+  return r;
+}
+
+int spdylay_submit_data(spdylay_session *session, int32_t stream_id,
+                        spdylay_data_provider *data_prd)
+{
+  int r;
+  spdylay_frame *frame;
+  frame = malloc(sizeof(spdylay_frame));
+  if(frame == NULL) {
+    return SPDYLAY_ERR_NOMEM;
+  }
+  spdylay_frame_data_init(&frame->data, stream_id, data_prd);
+  r = spdylay_session_add_frame(session, SPDYLAY_DATA, frame, NULL);
+  if(r != 0) {
+    spdylay_frame_data_free(&frame->data);
+    free(frame);
+  }
+  return r;
 }
 
 int spdylay_submit_request(spdylay_session *session, uint8_t pri,
-                           const char **nv)
+                           const char **nv, spdylay_data_provider *data_prd)
 {
   int r;
   spdylay_frame *frame;
   char **nv_copy;
   uint8_t flags = 0;
+  spdylay_data_provider *data_prd_copy;
   if(pri > 3) {
     return SPDYLAY_ERR_INVALID_ARGUMENT;
   }
+  data_prd_copy = malloc(sizeof(spdylay_data_provider));
+  if(data_prd_copy == NULL) {
+    return SPDYLAY_ERR_NOMEM;
+  }
+  *data_prd_copy = *data_prd;
   frame = malloc(sizeof(spdylay_frame));
   if(frame == NULL) {
+    free(data_prd_copy);
     return SPDYLAY_ERR_NOMEM;
   }
   nv_copy = spdylay_frame_nv_copy(nv);
   if(nv_copy == NULL) {
     free(frame);
+    free(data_prd_copy);
     return SPDYLAY_ERR_NOMEM;
   }
   spdylay_frame_nv_sort(nv_copy);
-  /* When we support POST using spdylay_data_provider, flags should be
-     0 if data_prd is set. */
-  flags |= SPDYLAY_FLAG_FIN;
-  spdylay_frame_syn_stream_init(&frame->syn_stream,
-                                SPDYLAY_FLAG_FIN, 0, 0, pri, nv_copy);
-  r = spdylay_session_add_frame(session, SPDYLAY_SYN_STREAM, frame);
+  if(data_prd == NULL) {
+    flags |= SPDYLAY_FLAG_FIN;
+  }
+  spdylay_frame_syn_stream_init(&frame->syn_stream, flags, 0, 0, pri, nv_copy);
+  r = spdylay_session_add_frame(session, SPDYLAY_SYN_STREAM, frame,
+                                data_prd_copy);
   if(r != 0) {
     spdylay_frame_syn_stream_free(&frame->syn_stream);
     free(frame);
+    free(data_prd_copy);
   }
   return r;
 }
diff --git a/lib/spdylay_session.h b/lib/spdylay_session.h
index d2a16ad..006516b 100644
--- a/lib/spdylay_session.h
+++ b/lib/spdylay_session.h
@@ -41,6 +41,7 @@
 typedef struct {
   spdylay_frame_type frame_type;
   spdylay_frame *frame;
+  void *aux_data;
   int pri;
 } spdylay_outbound_item;
 
@@ -123,9 +124,17 @@ typedef struct spdylay_session {
 
 /* TODO stream timeout etc */
 
+/*
+ * Adds frame |frame| of type |frame_type| to tx queue in |session|.
+ * |aux_data| is a pointer to arbitrary data. Its interpretation is
+ * defined per |frame_type|. When this function succeeds, it takes
+ * ownership of |frame| and |aux_data|, so caller must not free them.
+ * This function returns 0 if it succeeds, or negative error code.
+ */
 int spdylay_session_add_frame(spdylay_session *session,
                               spdylay_frame_type frame_type,
-                              spdylay_frame *frame);
+                              spdylay_frame *frame,
+                              void *aux_data);
 
 int spdylay_session_add_rst_stream(spdylay_session *session,
                                    int32_t stream_id, uint32_t status_code);
diff --git a/tests/main.c b/tests/main.c
index 8b6bb5d..6eda7f3 100644
--- a/tests/main.c
+++ b/tests/main.c
@@ -80,6 +80,8 @@ int main()
       !CU_add_test(pSuite, "session_send_syn_reply",
                    test_spdylay_session_send_syn_reply) ||
       !CU_add_test(pSuite, "submit_response", test_spdylay_submit_response) ||
+      !CU_add_test(pSuite, "submit_request_with_data",
+                   test_spdylay_submit_request_with_data) ||
       !CU_add_test(pSuite, "session_reply_fail",
                    test_spdylay_session_reply_fail) ||
       !CU_add_test(pSuite, "session_on_headers_received",
diff --git a/tests/spdylay_session_test.c b/tests/spdylay_session_test.c
index 77f93bf..8d6a902 100644
--- a/tests/spdylay_session_test.c
+++ b/tests/spdylay_session_test.c
@@ -220,7 +220,8 @@ void test_spdylay_session_add_frame()
   spdylay_frame_syn_stream_init(&frame->syn_stream, SPDYLAY_FLAG_NONE, 0, 0, 3,
                                 dup_nv(nv));
 
-  CU_ASSERT(0 == spdylay_session_add_frame(session, SPDYLAY_SYN_STREAM, frame));
+  CU_ASSERT(0 == spdylay_session_add_frame(session, SPDYLAY_SYN_STREAM, frame,
+                                           NULL));
   CU_ASSERT(0 == spdylay_pq_empty(&session->ob_pq));
   CU_ASSERT(0 == spdylay_session_send(session));
   CU_ASSERT(memcmp(hd_ans1, acc.buf, 4) == 0);
@@ -380,7 +381,7 @@ void test_spdylay_session_send_syn_stream()
   spdylay_session_client_new(&session, &callbacks, NULL);
   spdylay_frame_syn_stream_init(&frame->syn_stream, SPDYLAY_FLAG_NONE,
                                 0, 0, 3, dup_nv(nv));
-  spdylay_session_add_frame(session, SPDYLAY_SYN_STREAM, frame);
+  spdylay_session_add_frame(session, SPDYLAY_SYN_STREAM, frame, NULL);
   CU_ASSERT(0 == spdylay_session_send(session));
   stream = spdylay_session_get_stream(session, 1);
   CU_ASSERT(SPDYLAY_STREAM_OPENING == stream->state);
@@ -406,7 +407,7 @@ void test_spdylay_session_send_syn_reply()
                               SPDYLAY_STREAM_OPENING);
   spdylay_frame_syn_reply_init(&frame->syn_reply, SPDYLAY_FLAG_NONE,
                                2, dup_nv(nv));
-  spdylay_session_add_frame(session, SPDYLAY_SYN_REPLY, frame);
+  spdylay_session_add_frame(session, SPDYLAY_SYN_REPLY, frame, NULL);
   CU_ASSERT(0 == spdylay_session_send(session));
   stream = spdylay_session_get_stream(session, 2);
   CU_ASSERT(SPDYLAY_STREAM_OPENED == stream->state);
@@ -442,6 +443,33 @@ void test_spdylay_submit_response()
   spdylay_session_del(session);
 }
 
+void test_spdylay_submit_request_with_data()
+{
+  spdylay_session *session;
+  spdylay_session_callbacks callbacks = {
+    null_send_callback,
+    NULL,
+    NULL,
+    NULL
+  };
+  const char *nv[] = { NULL };
+  spdylay_data_source source;
+  spdylay_data_provider data_prd = {
+    source,
+    fixed_length_data_source_read_callback
+  };
+  my_user_data ud;
+
+  ud.data_source_length = 64*1024;
+
+  CU_ASSERT(0 == spdylay_session_client_new(&session, &callbacks, &ud));
+  CU_ASSERT(0 == spdylay_submit_request(session, 3, nv, &data_prd));
+  CU_ASSERT(0 == spdylay_session_send(session));
+  CU_ASSERT(0 == ud.data_source_length);
+
+  spdylay_session_del(session);
+}
+
 void test_spdylay_session_reply_fail()
 {
   spdylay_session *session;
diff --git a/tests/spdylay_session_test.h b/tests/spdylay_session_test.h
index 40742f0..29a7af4 100644
--- a/tests/spdylay_session_test.h
+++ b/tests/spdylay_session_test.h
@@ -33,6 +33,7 @@ void test_spdylay_session_on_syn_reply_received();
 void test_spdylay_session_send_syn_stream();
 void test_spdylay_session_send_syn_reply();
 void test_spdylay_submit_response();
+void test_spdylay_submit_request_with_data();
 void test_spdylay_session_reply_fail();
 void test_spdylay_session_on_headers_received();
 void test_spdylay_session_on_ping_received();