Spot-on insecticides are becoming a popular type of flea control for pets. Spot-on products available include those containing fipronil, imidicloprid, methoprene, and permethrin. Currently, over 15 brands of permethrin spot-on products are labeled for “use in dogs only.” These products contain high concentrations (45–65%) of permethrin insecticide and are becoming a very popular choice for flea and tick control for dogs. Cats are highly sensitive to permethrin and inappropriate or accidental application of these products would be fatal. Though they have a wise margin of safety when used appropriately on dogs, even small amount of permethrin spot-on products can cause severe clinical signs in cats. Indications of this species sensitivity have been documented by the National Animal Poison Control Center (NAPCC). In most cases, the owner applied the concentrated permethrin-containing poduct to cats accidentally or intentionally. In some situations, the exposure seems to have resulted when the product was used on the dog and cats were playing with dog. (ASPCA, NAPCC, Unpublished data, 1995–1997).