getting rid of form variable definition

What I am trying to do is send a varaiable, say "reauthenticate", from a form to change the username and password. So I'm trying something like if ($reauthenticate) { authenticate(); } The authenticate function exits and the script is recalled, but the variable $reauthenticate is still set so I can't get past this point. I guess the browser is sending back this variable each time. So how do you clear this variable? -Danny