<script language=javascript>
function disableCheck(obj) {
if (obj[obj.selectedIndex].className=='disabled') {
alert("선택하신 품목은 현재 절판입니다.");
for (var i=0; obj[i].className=="disabled"; i++);
obj.selectedIndex = i;
return;
}
}
</script>

<style type="text/css">
option.disabled { color: lightgrey; }
</style>

신발치수:
<select onChange="disableCheck(this)">
<option value='1'>260
<option value='2' class=disabled>270
<option value='3' class=disabled>280
<option value='4'>290
</select>