Anopheles gambiae mosquitoes were fed on 25 volunteers randomized to receive ivermectin or nothing. In mosquitoes feeding on volunteers given ivermectin the previous day, mean survival was 2.3 days, compared with 5.5 days in the control group (P < .001, by log-lank test). Mosquito mortality was 73%, 84%, and 89% on days 2, 3, and 4 in the ivermectin group. In mosquitoes fed 14 days after treatment, no difference was found between groups. Ivermectin is safe and has significant short-term insecticidal properties. A systemic insecticide taken by humans could help to control malaria in areas where mosquitoes are exophagic or exophilic and drug resistance is an urgent threat.