Our veternarian perscribed (and sold) the Frontline product to protect our two small dogs against fleas. We used the product in 2010 and 2011 with no problem. In 2012, for whatever reason, Frontline failed to perform as advertised. We returned the remainder of the medication to Merial with proof of purchase. Merial refused to honor their guarantee, giving us a "song and dance" about the product not being used "long enough" though the product is advertised as being a quick and effective treatment for fleas. Compare with Ortho Chemicals Flea Control guarantee: "if you are not satisfied for any reason, just send the purchase receipt for a full refund." In contrast, Merial exhibits a "public be damned" attitude.