[blackie007]

I think the mistake here is you introduce them too early before they got used to each other's scent.

The internet is a resourceful tool -- there's much you can learn from there. In Malaysia we don't have animal behaviourist to advise us, but you can get animal behaviourists' advise from the internet. And....they do not encourage caging the new cat and let the existing cats see it. In fact, they totally discourage any meeting at all, only introduce the scent indirectly (read my post no. 8).

They also advised giving the new cat and existing cats different food & water bowls, and different litter box. This is to prevent the existing cat from feeling that the new cat has come to take over. Feed the new cat in a separate room, and slowly, gradually, move the new cat's food bowl & existing cats' food bowls nearer and nearer the door that separates them.

Google and read up the articles written by professional animal behaviourists. I'm sure there are plenty of articles on what to do if you had not introduced your cats correctly the first time round. :)