I did some research two years ago on Frontline vs. Advantage (product improvements may have been made since then). In my opinion, Frontline is a better product for ferrets, simply based on the toxicity studies and adverse reaction reports from their testing on kittens. Both companies offer the disclaimer that their products have not been specifically tested for ferrets. Please, no flames about animal testing, and I also don't remember the EXACT numbers, but here's what I recall: On the kitten toxicity studies, toxic levels were reached at about 18xdosage for Advantage, and about 100xdosage for Frontline. This tells me that Frontline is far less toxic. Plus, Frontline kills ticks and Advantage does not. I have used Frontline (in half doses from the cat vial, which is 12-13 drops) for a few years on over 20 ferrets with no adverse reactions. I tried Advantage on 8 ferrets and got two with a rash, but that's it. The Frontline lasts for about 45-60 days at that half dose. - Erika Matulich and the Terrific Ten [Posted in FML issue 3041]