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In the submitted paper the (alpha-cyano-pyrethroid flumethrin was investigated concerning its clinical efficacy and mode of action against adult hard ticks, especiaIly under the aspect of its aptitude as an antiparasitic agent in dogs. The active ingredient was solved in different concentrations in a spray formulation, respectively used as a 95% pure substance which was diluted in solvents.The efficacy through contact with the substance after topical application via filterpaper showed an efficacy on vitality of 98% to 100% against different unfed hard tick species using a concentration of 9 pg/tick flumethrin in a spray formulation. There was no effect observed on fully engorged Rhipicephalus ticks concerning vitality. The contact efficacy was confirmed in a dose titration and a dose confirmation study on Retriever-Labrador dogs. The 0,30% mN flumethrin spray formulation in a dosage of 9 mg/kg body weight showed a repellent efficacy up to five weeks, a curative efficacy against an established tick infestation within wo days post treatment of 100% and a residual activity against reinfestations with ticks of >95% for five to six weeks following treatment. The results of these studies were also confirmed in a field study in different investigation sites in France and Germany on 114 dogs treated with flumethrin-spray (efficacy rates of 98.7% for therapeutic and 99.5% for residual activity).Flumethrin-spray had no systemic efficacy on vitality against ticks, when injected abdominally in a dosage of 30 pg respectively 90 pg in fully or partly engorged ticks during 48 hours following treatment. In concentrations up to 300 mg/1 flumethrin in cattle blood, the substance was fed through artificial membrane feeding to attached Ixodes ricinus, without having an effect on the vitality of the ticks. After dermal treatment with flumethrin spray formulation, no flumethrin could be detected in the serum of dogs after day +4 post treatment.Together with the in vitro results it could be concluded that flumethrin has no systemic activity against ticks and that its very good clinical efficacy against ticks is only caused by contact.