Maximum amount of variables in a session?

Hey everyone... I am creating a project for a web hosting control panel and just wondering if there is a limit to the amount of variables I can store in a session? If I have too many variables will it create an uneccassary strain on my server? What is an average amount of variables that a session should have. I have a good knowledge of basic PHP but have never worked with sessions before. This project is a learning project and a project because I have yet to find what I'm looking for in hosting control panels. Richard Marriner Maingear Networks http://www.maingear.net