<?xml version="1.0" encoding="utf-8"?>
<!-- http://blog.flexexamples.com/2008/01/26/displaying-item-tool-tips-in-a-flex-combobox-control/ -->
<mx:Application xmlns:mx="http://www.adobe.com/2006/mxml"
        layout="horizontal"
        verticalAlign="top"
        backgroundColor="white" viewSourceURL="srcview/index.html">

    <mx:Script>
        <![CDATA[
            private function init():void {
                comboBox2.dropdown.toolTip = comboBox2.toolTip;
            }
        ]]>
    </mx:Script>

    <mx:Array id="arr">
        <mx:Object label="Lorem ipsum dolor sit amet, consectetuer adipiscing elit." />
        <mx:Object label="Donec sit amet dui nec pede aliquam auctor." />
        <mx:Object label="Integer vestibulum sodales dui." />
        <mx:Object label="Sed nonummy ligula et tortor." />
        <mx:Object label="Aenean varius neque vel felis." />
        <mx:Object label="Phasellus venenatis ipsum sit amet nisi." />
        <mx:Object label="Nullam vitae turpis et ipsum cursus venenatis." />
        <mx:Object label="Pellentesque tincidunt pede non arcu." />
        <mx:Object label="Aliquam ut massa quis ante dignissim egestas." />
        <mx:Object label="Curabitur facilisis velit sit amet metus." />
        <mx:Object label="Vivamus ornare massa ac massa." />
        <mx:Object label="Nam accumsan rutrum purus." />
    </mx:Array>

    <mx:ComboBox id="comboBox1"
            dataProvider="{arr}"
            toolTip="Please select some text."
            width="200" />

    <mx:ComboBox id="comboBox2"
            dataProvider="{arr}"
            toolTip="Please select some text."
            width="200"
            creationComplete="init();" />

</mx:Application>