Permethrin 1% creme rinse (NIX) was tested as a treatment for Pediculus humanus var capitis (head lice) in a placebo-controlled, double-blinded, randomized study. As a positive control, a third arm of the study included nonrandomized, but investigator-blinded, treatment with 1% lindane shampoo (Kwell). At 14 days after treatment, 97% of patients treated with permethrin were free of lice compared to 6% of placebo-treated patients (P less than 0.001) and 43% of the lindane-treated group. Permethrin was 70% ovicidal compared to 14% for placebo (P less than 0.001) and 45% for lindane. No adverse experiences were noted during this study. Permethrin 1% demonstrated high pediculicidal and ovicidal activities, which in combination with its low mammalian toxicity, residual activity, and cosmetic properties, make it an excellent treatment for pediculosis capitis.