If you do have an infestation, you will need to treat the whole house. Apparently for every 5 fleas you see on the dog there are another 95 in the house waiting to hatch out and jump on the dog! I used something called Indorex which you put down and then hoover every day for a minimum of 7 days. The Frontline still protects the dog it just takes 24 - 48 hours to kill the fleas that land on the dog which is why you see them. According to my vet this has been the worst year for fleas, they are doing a roaring trade in flea products. I suffered an awful infestation earlier this year, and have never had a problem before, but this treatment did work and banish them once and for all. Good luck, hope you manage to get them cleared up