My roommate works at a vet and gives my ferrets 1/2 a dose of the kitten Advantage to their necks. So, one dose for a kitten is good for two ferrets. The advantage goes by their weight. As, far as we know their is not one designed for ferrets and we were a little leary of giving it to ours, but they do fine. Apparently it tastes very bad, so they don't lick it off each other or anything. It did help rid the flea problems we were having when nothing else seemed to. If you do try Advantage make sure to wash all of their beddings etc. There may be flea eggs in them. [Posted in FML issue 2140]