Use bindable string variable to set the Label text
<?xml version="1.0"?> <mx:Application xmlns:mx="http://www.adobe.com/2006/mxml" creationComplete="checkEI()"> <mx:Script> [Bindable] public var eiStatus:String; private function checkEI():void { eiStatus = ExternalInterface.available.toString(); } </mx:Script> <mx:Label id="l1" text="{eiStatus}" /> </mx:Application>