I just recently purchased a 6 month supply of Frontline for my Cat because she has a flea problem. I purchased the 6 month supply because i had purchased Frontline before and to my knowledge it had worked. Well not this time, i did apply it correctly, however this time it did nothing at all to kill the fleas on my Kitty. Now I'm stuck with the remainder of the package and really wish i could just get my money back. Advantage however, has always worked properly and i have never had a problem with it, but since Amazon had Frontline with free shipping, i went that route trying to save some money. Big mistake! Just wanted to warn people, if you have never tried frontline before, buy a single dose first and see if it's going to work for you so your not out a lot of money if it doesn't.