Sessions and Forms

Hey all, Does anyone know if setting a session has any effect on forms. when I put session_start() at the top of my files with a form in, it does not keep the values for the form when pressing back. i.e. if someone makes a mistake on a form and has to go back the values they had entered are gone. However if I take the session_start() out again and press back everything is fine. Thanks a million Phil Caint.com