help with _PHP_SELF and changing a paramter in URL...

sorry, it's late gotta get some sleep, but this had been stumping me... have to change a value in the URL, say: www.foo.com/test.php?var1=10&var2=10 i want to make that a clickable link but set var1 = 20. i'm getting tired so i may not be searching php.net correctly... would i EREGI_REPLACE it or some other way? the link i want to set it is www.foo.com/test.php?var1=20&var2=10 thanks... -- Leo G. Divinagracia III ldivinag@csuhayward.edu