Problems adding extra session variable to login

Nubie....
I want to pass another field as a session variable from the php login exetension
I have edited this line:

$LoginRS__query=sprintf("SELECT userName, userPassword, sugarID FROM users WHERE userName=%s AND userPassword=%s",

and then added the following

$_SESSION['MM_sugarID'] = $sugarID;
$_SESSION['MM_Username'] = $loginUsername;
$_SESSION['MM_UserGroup'] = $loginStrGroup;

I am unable to read the session variable sugarID in my authenticated page.
Can anyone help - am I adding the stuff in the right area
Thanks for you help in advance