I have to say that I have always found frontline to be a very effective method of controlling fleas.However in saying that I also feel that if you continue to use repeated applications the fleas start to show immunity.I personally have not struck this problem yet.If you are not happy using chemical methods garlic powder sprinkled or mixed on their food can help.However not when you suffer from major infestations,then it is time to treat with other methods.Don't forget to worm your cat when you de-flea.One of my current moggies corny she literally has to be wrapped tightly to apply the frontline as if she is not you end up needing plasters to stop the bleeding lol.Corny literally hates having it applied and will run a mile if she sights you coming with the little pipette.My other two don't care in the least when I'm applying the frontline.