Metronidazole in obstetrics and gynecology has been investigated. 200 gynecology patients were studied 1/2 of them were controls and the others received prophylactic metronidazole. 155 patients were included in the obstetrical study. Prophylactic metronidazole for patients undergoing hysterectomy eliminated the overt anerobic infections which otherwise occur in over 20% of these women. Convalescence was much smoother than in patients with clinical infections where there is a high incidence of minor morbidity due to anerobes. Generally anerogic infection is of relatively minor importance in normal obstetrics but is more common following cesarean section. A regimen for the minimum totally effective dose of metronidazole for use in prophylaxis includes a 1200 mg preoperative dose followed by 1 gm every 8 hours for 48 hours postoperatively.