I have done a small sample on how to use the C# Javascript Wrapper in web applications to get new data without the need of a postback. Feel free to download the sample from http://schwarz-interactive.de/download/clientcallback.zip [1]. Unzip the file, create a virtual IIS folder and start the application. The methods used in the default.aspx can be found in default.aspx.cs. They are marked with an attribute (MS.Web.JavascriptMethod). Currently you can use bool, int, string and XmlDocument for the return value, more later.