Thanks for the ideas. I actually work at a veterinary emergency facility (have for over 8 years)....Neither is sick, neither have been to the vet recently...I thought of that too, but as much as I rack my brain, there is absolutely nothing that has changed in their life, environment, surroundings, etc...I just can't figure it out! I have some feliway spray, I may try spraying it on a towel and rubbing both cats as well in an attempt to calm whatever is going on between these two. Any other thoughts and/or suggestions would be greatly appreciated, I just want to get them back to where they were before this happened.