Multiple Key Presses ( AS3 )

How can we know when 2 keyboard keys are pressed at the same time, example LEFT and UP keys?
I read the first 3 pages of this:
http://www.kirupa.com/developer/actionscript/multiple_key_detection.htm
but the tutorial centers on the ctrl + keyCode only.
this does not work ( only detects 1st key / one of the keys pressed ):

stage.addEventListener( KeyboardEvent.KEY_DOWN, handleKeyDown );

function handleKeyDown( event:KeyboardEvent ):void {
// LEFT = 37, UP = 38, RIGHT = 39, DOWN = 40
if ( event.keyCode == 37 && event.keyCode == 38 ) {
trace( " huraaah! " );
}
}