I've tried several things and the one that works the best for me is Advantage. If there is a huge flea problem, you can get CapStar from your vet. It's a tiny pill. After administering it, within about 1/2 hour the fleas drop off. However, it's not a longterm solution. Using Advantage with the CapStar keeps the fleas under control. That and vacuuming and spraying the house. I got a flea spray (Mycodex) from my vet. The cats can re-enter the sprayed room after an hour.