<html>
<head>
<title>prova</title>
<script language="javascript">
<!--
function ale(){
var lng=document.myForm.TIPO.length;
var messaggio="";
for(var i=0;i<lng;i++){
if(document.myForm.TIPO[i].selected){
messaggio+="Selezionato: "+document.myForm.TIPO[i].value+"\n";
}
}
alert(messaggio);
}
//-->
</script>
</head>
<body>
<form name="myForm">
<select name="TIPO" size="7" multiple id="TIPO">
<option value="0" selected>Tutti</option>
<option value="1">Basso rischio</option>
<option value="2">Medio rischio</option>
<option value="3">Alto rischio</option>
<input type="button" onClick="ale()" value="Controlla">
</form>
</select>
</body>
</html>