Memory used by script...

Hi... I got a big site, which is not very well constructed inside, and the script began to throw (rather often, but NOT always) a fatal error " Fatal error: Allowed memory size of 8388608 bytes exhausted ", every time in different places. I wonder how should I debug that, as there is pretty much code inside, and I hardly got aqcuainted with it in a whole. SO THE QUESTION: Are there any functions or smth., to check, how much memory is used at some particular moment of execution of the script??? If I could state, that for example after some class instantiaton memory usage greatly increases, I would be able to localise the problem. Thanks much, Mark. Do not hesitate to send Your reply's also on mark@ebi.lt.