note 3107 deleted from function.session-start by sniper

What session_start does is looks for an existing session, and if none exists, it creates a new one. What it also does (that wasn't fully eplained above by the statement "initializes variables" is looks for any session variables, and sets them globally on the page that start got called from. If you have any variables already set (say from a get/post from the previous page) they will get overwritten. Also, changing a variable on a page will not update its session counterpart. Also, note that any call to session_register will automatically call session_start (and therefore pull all session variables and set their local counterparts.) If I wasn't so lazy, I'd upload an example of what I mean.