Hello. Straight to the point: I have this javascript: for(item=1;item<5;item++) { xmlhttp=new XMLHttpRequest(); xmlhttp.open("GET",'zzz.php', true); xmlhttp.send(); } And in PHP file something like this: usleep(5);die('ok'); Now the problem is javascript seems to be waiting for each ajax call to be completed before sending another one. So the first response gets back after approx. 5 seconds, next after 10 seconds and so on. That's a very simplified version of what I do, since the real script involves using cURL in PHP and jQuery as JS lib. But the problem remains the same. Why do responses come back in 5 second intervals?