Mariner - though it is impossible to diagnose from a brief description like that (and Im not qualified anyway), I will say that it sounds like your friend does need some help. Paranoia can be a symptom of depression, but is usually accompanied by more of the other recognisable signs. It can also be a symptom of other mental health problems / illnesses - some of them very serious. If I were you, I would speak to a doctor yourself and see if they can advise you on what to do for the best - ie how to persuade your friend to get help when he thinks there is nothhing wrong with him. And don't be fobbed off. If one doctor can't help, try to speak to another one.

Good luck and keep me up to date?

Bagpuss