I got a new kitten a couple of months ago. My almost four year old cat hated him, and I thought she would try to kill him if left unsupervised. After a couple of weeks of keeping them separated and bringing them together for brief meetings, they were eventually able to share a space together without a problem. In fact my cat was acting like the kitten's mama--constantly grooming him and even playing with him. She had no problem with the kitten bugging her, snuggling, plopping down on top of her, etc. All was right with the world until I brought the kitten home from the vet this morning. He was neutered yesterday and had to stay overnight at the vet. When I brought him home, I expected that my cat would hiss at him a little, because of the different smells at the vet's office. I thought that because she had been like a mama to him though, that she would get over it fairly quickly once she recognized him. However, it is worse than I thought it would be. She has been hissing, growling, trying to bite him, and stalking him like prey all day. The little kitten looked so hurt when he tried to snuggle and she attacked him. They are currently separated, and I am worried that I may have permanently damaged the relationship by letting the kitten in her space as soon as he got home, but like I said I didn't think it would be that bad. I am worried that I will have to start the long introduction process all over again. It is even worse than when they met the first time. I have already tried rubbing them with the same towel (it just made my cat angry), and I am familiar with site swapping (I watch My Cat From Hell). I have not tried Feliway. I just have the kitten isolated for safety right now. Has anyone else had a similar problem when bringing a kitten home from the vet after being fixed, and if so, how long did it take for the angry cat "to get over it"? Does anyone have a cat that never got over it?