 <p>You do this by using a string:</p> <pre><code>&gt;&gt;&gt; class Node(messages.Message): ... name = messages.StringField(1) ... children = messages.MessageField('Node',2,repeated=True) </code></pre> <p>You can see an example of this in the echo service demo here:</p> <p><a href="https://github.com/google/protorpc/blob/master/demos/echo/services.py#L81" rel="nofollow">https://github.com/google/protorpc/blob/master/demos/echo/services.py#L81</a></p>