It was IE5 AFAIR. EDIT: And to be precise, XMLHttpRequest is Mozilla's naming that came later (after Microsoft's interface name: IXMLHTTPRequest). So you meant

It was IE5 AFAIR. EDIT: And to be precise, XMLHttpRequest is Mozilla's naming that came later (after Microsoft's interface name: IXMLHTTPRequest). So you meant: ActiveXObject("Microsoft.XMLHTTP")