Load testing ajax application using Visual Studio 2010

In order to do this, you need to extend Visual Studio Web Performance Test  with your own Extraction and/or Validation Rule. Visual Studio 2010, which my current working copy, has all interfaces provided for the needed customizations.

Here is an official tutorial for Creating a Custom Extraction Rule, which can lead you to the place where you can find all useful information and a real code example.

For java users, you may want to explore HtmlUnit platform.