Because malathion resistance in the human head louse is very widespread in the United Kingdom,1 it is inevitable that malathion resistance will also eventually develop in other countries where it is used or has been reintroduced, such as in the United States.2 When applied to susceptible insects, a product with a second, added insecticide with a different mechanism of action will reduce the chance of insecticide resistance developing to either insecticide.3 Because we have shown4 with in vitro exposure tests that α-terpineol (and other monoterpenoids) are effective pediculocides, we investigated the effectiveness of Ovide (Taro Pharmaceuticals, Hawthorne, NY), a 0.5% malathion in isopropanol lotion containing 3 additives (α-terpineol, dipentene, and pine-needle oil), and an Ovide vehicle (without malathion) on British malathion-resistant head lice to see whether they kill these lice.