doing it on the carpet

2 months ago I took possesion of a 9 year old ginger tabby from my friend.
He had 4 cats but when moving to a smalller house he couldn't take the 2 brothers because they fought.
He is a house cat and only steps outside for a look around.
Initially he used the litter tray but has since decided to start using the carpet for his toilet.
I've tried a few different litter combinations but with no luck so far.
Apart from his bad toilet habits he's happy around the house.
What can I do now?

Thanks
Raymond

If there are no health issues, he's doing it there because he can smell the kitty toilet there. Is it a particular spot in the carpet? What do you use to clean the carpet?

As Yayi mentioned, the first thing to do is have him in to see his vet for a checkup and rule out any underlying health issues. If he is otherwise healthy and happy, there are many good ideas contained within this thread:

http://www.thecatsite.com/forums/showthread.php?t=9563