Okinawa Prefecture is an endemic area of Strongyloides stercoralis infection. Since treatment of this infection remains unsatisfactory, we evaluated the efficacy of ivermectin. Twenty-three patients were treated with a single oral dose of ivermectin (mean +/- SD, 105.5 +/- 20.8 mcg/kg of body weight), followed by a second dose two weeks later. The rate of cure was 85.7% at 2 weeks after the first treatment, and 90.5% at 2 weeks after the second treatment. Side effects occurred in 2 patients (8.7%), but they were mild and transient. The results indicate that ivermectin might be useful and relatively safe for the therapy of Strongyloides stercoralis infection as an alternative to thiabendazole or mebendazole.