Is it possible that people do another PhD after they have completed one PhD? what are the requirements?

I should think the main requirement would be insanity, it's hard enough to do it once! ;o)

Agree with Anne!! However it has been known to happen.

A PhD is a training for a career in research. Once you have this training you should be able to find a research job, to allow you to complete any further research aims. Another PhD would seem pointless.

I agree with the find a phd team but i know someone who has alrady got 2 phd and working towards his 3rd one and he is not even 40 yrs old

if you think to carry your studies further away you should apply for PosDoc after completing the PhD. Not doing another PhD.

Fourth PhD?????
Now THAT is sad.

Whoops! I meant THIRD PhD!!

Are you sure that he is not buying them off the internet? ;oD

So what's the going rate for one these days?

Unless it was in another field, multple PhD's are just progressing a career sideways. As previously stated, doctoral training (PhD) is usually followed by post doctoral training.