 <p>The short answer is "no". Unless you're talking about a very long running backgrounded process on the server side, in which case you could have a second Ajax request initiate a stop on it. But if you're talking about a regular request to an Apache/PHP server, then no... identifying which Apache thread your request was running in would be trouble enough.</p> <p>It would be much easier to verify your Ajax request somehow before even starting the process; make sure it's what you want to be running. You could have a Javascript confirmation process as well if you need the user to be aware that what they are doing cannot be interrupted.</p> <p>As Steven posted, having a reversal process sounds like it might be in your best interest as well.</p>