I don't see any errors in Firebug, and I can't figure out what's wrong with the AJAX.
PHP:
<?php
$subject = $_POST['subject'];
echo $subject;
?>
Javascript
<html>
<head>
<script type="text/javascript">
/* <![CDATA[ */
function ajax() {
if (window.XMLHttpRequest) {
xmlhttp=new XMLHttpRequest();
} else {
xmlhttp=new ActiveXObject("Microsoft.XMLHTTP");
}
xmlhttp.onreadystatechange=function() {
if (xmlhttp.readyState == 4 && xmlhttp.status == 200) {
document.getElementById("result_div").value = xmlhttp.responseText;
}
}
xmlhttp.open("POST","message.php",true);
xmlhttp.send();
return false;
}
/* ]]> */
</script>
</head>
<body>
<div id="result_div"></div>
<form action="" onsubmit="return ajax();">
<select name="teest">
<option value="hi">hi</option>
</select><br />
<input type="text" name="subject"> <br />
<input type="submit">
</form>
</body>
</html>