Let me preface this by saying that I am working on an application that I did not write. If that had been the case, i would not have made the decisions that are causing this problem. That being said......The application is using cache and session to store datatables, controls, and (gasp) viewstate information. I am noticing that the session drops when users perform certain actions. After digging around i found that the viewstate for the page keeps growing when performing ajax postbacks from an Infragistics webgrid. When i navigate to a different page and navigate back, the viewstate (in session) is refreshed. So, i was wondering, do the html changes just get appended to the viewstate on ajax postbacks instead of actually refreshing it?