I heard you are not suppose to use Frontline on Ferrets. Just Advantage. Make sure if you are using the dog strength, you have to use less. Make sure the concentrations are the same. I use the cat, under 9 lbs. There is a link for cheaper advantage, 4 tubes for 19.99. Shipping not bad either. Here is the link: www.petshed.com Marguerite (The Internet Queen of Finding Good Deals!) And her Crew 10 Fuzzy Ferrets 12 Fuzzy Ferret Rescues [Posted in FML issue 4339]