A total of 39 patients was admitted to the obstetric and gynecological wards of Nagoya University Hospital and the University's 5 related hospitals during the period from July 1981 to March 1982. The efficacy of cefoxitin sodium was evaluated in the 39 patients with a wide variety of obstetric and gynecological infections. The findings are the follows: Of the 39 patients, the responses in 7 were judged "excellent", 28 "good" and 4 "poor" with the clinical efficacy rate of 89.7%. The causative pathogens in 23 of the cases were isolated from clinical materials submitted to the Institute of Anaerobic Bacteriology, School of Medicine, Gifu University. In these 23 cases, it was found that 8 were due to aerobic bacteria only (34.8%), 8 mixed aerobic-anaerobic bacteria (34.8%) and the remaining 6 anaerobic bacteria only (26.1%), i.e. a substantial percentage (60.9%) was due to anaerobic bacteria or mixed aerobic-anaerobic bacteria. Cefoxitin was active against most strains of Bacteroides spp. and was not affected by the inoculum size. On the other hand, most strains of Bacteroides spp. were resistant to cefazolin when the inoculum size was increased from 10(6)/ml to 10(8)/ml. Lincomycin was also found to be active against many fo the strains of Bacteroides spp. Cefoxitin and cefazolin were fairly active against anaerobic bacteria other than Bacteroides spp., while these same bacteria were resistant to sulbenicillin and many of them showed resistance to lincomycin. Cefoxitin was well tolerated and no untoward side effects were observed. The clinical and bacteriological results indicate that cefoxitin is a very effective antibiotic in the treatment of a wide variety of obstetric and gynecological infections and is a suitable choice as initial antibiotic therapy in these conditions.