Before 1961 the authors used many different methods of treating Trichomonas vaginalis infections. Despite this search for adequate therapy, long-term results remained poor. However, simultaneous systemic chemotherapy of both husband and wife, using the recently developed trichomonacidal drug metronidazole, has produced excellent results. The patients in this study have been checked periodically from 1 to 18 months after treatment. Careful evaluation of blood and urine, liver function tests, and physical examination have not revealed any evidence of toxicity.