Cefoxitin (mefoxin), a new semisynthetic cephamycin antibiotic, is resistant to degradation by β-lactamase enzymes produced by bacteria. In vitro, cefoxitin is active against virtually all clinically important gram-negative facultative bacteria other than Pseudomonas and Enterobacter spp., gram-positive aerobic bacteria other than the enterococcus, and clinically important anaerobic organisms, including Bacteroides fragilis. This broad antibacterial spectrum suggested that cefoxitin might be an effective single antibiotic agent for the treatment of mixed aerobic-anaerobic infections in obstetric and gynecologic patients. In this investigation, the efficacy and safety of cefoxitin was evaluated in 109 patients'68 with salpingitis, 25 with endomyometritis, 9 with pelvic cellulitis, and 7 with pelvic abscesses. An average of 2.5 bacteria were isolated from each patient. Aerobic bacteria alone was isolated in 38% of patients, anaerobic bacteria alone in 25%, and a combination of aerobic and anaerobic bacteria was isolated in 37% of patients. Overall, 100 of 109 (92%) infections responded to treatment with cefoxitin alone. The major cause of treatment failure was the presence of abscesses requiring surgical drainage. In addition to being an effective single agent for the managment of pelvic infections, cefoxitin proved to be safe and well tolerated by patients.