Oh, i can confide with you on this one! Fiona had fleas all summer last year, so this year i was on top of it, put frontline plus on her right in june and then she was covered! we went to the vet last month, and she got switched to revolution, and i'm still having a flea problem. its soooo annoying, we have treated the house, yard, cats, dogs, and her, and still......ahhh!!!!!!