查询Web服务以获取消息列表？

Is there a straightforward way to query a web service to see which messages it supports? The C# .NET application I'm working on needs to be able to handle an older version of the web service, which does not implement the message I'm trying to send. The web service does not expose a version number, so Plan B is to see if the message is defined.Is there a straightforward way to query a web s