Well it's nice to know I'm not the only one w/this problem. Charlie outweighs Colby. When I had both Mimi & Colby, there was a somewhat similar problem w/Mimi attacking Colby at times. A friend said try saying "NO" to Colby when Mimi would attack her. The idea was that I was acknowledging to Mimi that she was the dominant cat. I tried it the next time it happened and I have to admit, things changed quite a bit after that. Now whether it really worked or was just a coincidence, I don't know but Mimi stopped attacking Colby. I've tried the same thing w/Charlie and Colby but to no avail. Thanks all for your replies. A friend here at work told me about this site and I love it! Cats rule (of course, they've ALWAYS known that).