[Zope] Zope speed

Hi all ! I have a zope site working with apache, and all works fine !! Still, making the exact same requests, the time to respond is mostly different ! sometimes a request is given like a bullet, but on the other side, it takes a lot of time ! (there are only two clients connected to the server) Is there any way of monitorize zope requests ? Has anyone had this kind of situation ? Best regards to you all Nuno