Puoi fare cosi

codice:
<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN">

<html>
<head>
<title>Untitled</title>
<script language="JavaScript" type="text/javascript">
<!--
function listList(aSelect) {
 for (i=0;i<aSelect.length;i++) {
  curOpt = aSelect.options.item(i);
	valore = curOpt.value;
	testo  = curOpt.text;
	alert('Valore = '+valore+' - Testo = '+testo);
 } // function listList(aSelect) 
} // function listList(aSelect) 
//-->
</script>

</head>
<body>
<select size="8" id="sel">
 <option value="1">aaaaaa</option>
 <option value="2">bbbbbb</option>
 <option value="3">cccccc</option>
 <option value="4">dddddd</option>
 <option value="5">eeeeee</option>
 <option value="6">ffffff</option>
</select>
<input type="button" value="Lista" onclick="listList(document.getElementById('sel'))"/>
</body>
</html>