<script type="text/javascript" language="javascript">

var http_request = false;
function makeRequest(url) {

http_request = false;
if (http_request.overrideMimeType) {
http_request.overrideMimeType('Content-Type: image/png');
}

if (window.XMLHttpRequest) { // Mozilla, Safari,...
http_request = new XMLHttpRequest();
if (http_request.overrideMimeType) {
http_request.overrideMimeType('text/xml');
}
} else if (window.ActiveXObject) { // IE
try {
http_request = new ActiveXObject("Msxml2.XMLHTTP");
} catch (e) {
try {
http_request = new ActiveXObject("Microsoft.XMLHTTP");
} catch (e) {}
}
}

if (!http_request) {
alert('Poddaję się :( Nie mogę stworzyć instancji obiektu XMLHTTP');
return false;
}
http_request.onreadystatechange = function() { alertContents(http_request); };
http_request.open('GET', url, true);
http_request.send(null);

}

function alertContents(http_request) {

if (http_request.readyState == 4) {
if (http_request.status == 200) {
document.getElementById("test").innerHTML = http_request.responseText;
} else {
alert('Wystąpił problem z zapytaniem.');
}
}

}

idInterwału = setInterval("makeRequest('test.php')", 3000);

</script>
<div id="test"></div>

<BR><a href="ajax.php" onmouseout="idInterwału=setInterval('makeRequest()', 3000)" onmouseover="clearInterval(idInterwału)">Stop</a><BR>