This is a follow up post to a prior post (note to Hissy, I assume it is OK to post a new thread because it has to do with dealing with aggression rather than the cause). At any rate I have three spayed, female cats. Essie, age 4, is the mother of Stinkerbelle and Mukluk (both 3 years old). I have had them for about 2 and a half years and all got along great until last Saturday (5/14) when Essie went ballistic and attacked Stinkerbelle. After all three went to the vet on Monday (the 16th) and were deemed healthy, as recommended by the vet, I installed a feliway diffuser in the living room (two bedroom apartment) that day. I have also been using feliway spray 1-2x daily in the two bedrooms. My cats have settled down to some extent (most recently, 12 hours of getting along together) but I am still having episodes of growling and hissing (and two more "ballistic" attacks in which case the cats were immediately separated). Stinkerbelle seems to be most likely to growl at Essie, Essie responds by becoming aggressive, Mukluk will hiss if the other cats get aggressive, but she does not seem to start things). My question is, should I immediately separate them when they growl or hiss at each other- or should I wait a few minutes to see if they settle down? So far if it looks like an attack is imminent, I have been separating them, other times the growling and hissing abates and they seem OK after that. If it does not seem like an attack is going to happen should they be separated anyway? If so, how long should they be kept apart? Assuming I continue having problems with aggressive behavior among these cats, how long should I wait before considering some type of medication for one or more of these cats? They have a follow up with the vet on June 6th. Thank you in advance for any advice that can be offered.