diff --git a/README.md b/README.md
index ff962a0..00191ea 100644
--- a/README.md
+++ b/README.md
@@ -53,8 +53,9 @@ Get a member's details.
 ### get_messages()
 Get all your messages.
 
-### send_message(chat_id, text)
-Send a message with content `text` in a specific chat with id `chat_id`.
+### send_message(text, user=None, group_uid=None, chat_id=None)
+Send a message with content `text`.
+Either specify an existing `chat_id`, or both `user` and `group_uid` for a new chat.
 
 ## Example scripts
 
diff --git a/spond/spond.py b/spond/spond.py
index eeafd12..d342f3e 100644
--- a/spond/spond.py
+++ b/spond/spond.py
@@ -162,7 +162,10 @@ async def _continue_chat(self, chat_id, text):
 
     async def send_message(self, text, user=None, group_uid=None, chat_id=None):
         """
-        Starts a new chat or continue old one.
+        Start a new chat or continue an existing one.
+
+        If `chat_id`of an existing chat is specified, message continues that chat.
+        Otherwise, both `user` and `group_uid` must be specified, and the message starts a new chat.
 
         Parameters
         ----------