A controlled clinical trial was carried out to assess the mortality and repellency of a new topical combination of f ipronil-permethrin (Effitix® Virbac, Mexico) against Rhodnius prolixus in dogs. Ten medium-size dogs (10−15kg) with short hair were used. The dogs were exposed to 8 adult triatomines once weekly for 7 weeks. On the control day (D0), the dogs were exposed to the insects without treatment. On D7, the dogs were immediately treated with a spot-on 2.2ml pipette containing 134mg of fipronil and 1200mg permethrin after exposure to the insects. The dose was repeated after 4 weeks following the manufacturer’s instructions. Repellency at D0 was, 0 % and the insects had a high blood content. After 12h post-contact, repellency was 86.3 % and slowly decrease though D21 and D28. On D7, none of the insects survived after 3h of feeding on the treated dogs. On D14, D35 and D42, all insects died within 12h post-feeding, whereas no mortality was observed in the control D0 (P < 0.05). The results of this study indicated that administration of the product following the manufacturer’s instructions was efficacious at inducing rapid mortality of R. prolixus and therefore could be useful to prevent the transmission of American trypanosomiasis in dogs.