The mainstays of treatment of body-louse infestation in humans in a community setting are insecticides and the removal of infested clothing. We report here the dramatic effect that 3 doses of oral ivermectin (12 mg each), administered at 7-day intervals, have in reducing the total number of body lice in a cohort of homeless men from a shelter in Marseilles, France. We identified a baseline total of 1898 lice in the cohort. Over a 14-day period, this number fell to 6 lice; the prevalence of infested individuals fell from 84.9% to 18.5%. Although this effect was not sustained at day 45, it establishes that ivermectin plays a novel role in the control of body-louse infestation in humans.