Increased understanding of bacterial infections of the pelvis has led to the frequent administration of double and triple antimicrobial chemotherapy for polymicrobial infections in hospitalized patients. This study evaluated the use of high-dose cefamandole as a single agent in the treatment of obstetric and gynecologic infections. Cefamandole was administered by intravenous infusion of 2 gm every 4 hours or, less often, every 3 hours. Twenty patients were entered into the study, 11 with postpartum endometritis and nine with pelvic inflammatory disease. Seventeen of the 20 patients (85%) were successfully treated; all failures were in the endometritis group. The aerobic organisms and the gram-positive anaerobic organisms isolated from these infections were susceptible in vitro to cefamandole at attainable serum concentrations. The bacteroides isolated were more resistant. The data suggest that high-dose cefamandole therapy is effective as a single agent for the majority of moderate obstetric and gynecologic infections.