>I have a .NET WebService that authenticates a caller by checking the username and password that are required to be passed in the SOAP header. I would also like to be able to check the caller’s IP address. I’ve tried using HttpContext.Current.Request.UserHostAddress, but this appears to return the IP address of the server where the WebService resides, not that of the calling client.

Try:

HttpContext.Current.Request.ServerVariables("REMOTE_ADDR")