Metronidazole was used to treat 116 patients infected with Dracunculus medinensis. The patients had lesions of all four basic types: cryptic, preblister, blister, and ulcer. The drug was given orally, in three 200-mg doses a day, for 7 days. Fever, pain and swelling subsided and disability ceased within the week of therapy in 108 patients, and in the remaining 8 during the following week. Of 96 patients with moderate to severe lesions, healing was complete in 26 within the first week, in 41 in the second, in 18 in the third, and in 8 in the fourth; there were 3 failures. Patients with mild lesions (20) became symptomless in a few days. Subcutaneous worms appeared to be irritated by the drug, sometimes migrating and disappearing. Worms were either expelled from ulcer lesions (46) during the first two weeks (25) or were painlessly extracted (21). Cellulitis in 12 patients seemed to interfere with the action of the drug and required procaine penicillin therapy and minor surgery. Side-effects were mild and did not persist beyond the treatment period. Although metronidazole appears to be more effective than diethylcarbamazine, niridazole, or thiabendazole in the treatment of dracunculiasis, controlled, comparative trials of the four drugs should be done.