Cefpimizole (AC-1370), a new cephem antibiotic, was studied in the field of obstetrics and gynecology, and the following results were obtained. The absorption and tissue penetration of AC-1370 into intrapelvic genital organs were good. The peak serum level in the uterine artery after an intravenous drip infusion for 30 minutes was 49.0 micrograms/ml. High concentrations were obtained also in genital organ tissues; the maximum concentrations were 24.4 approximately 39.0 micrograms/g after an intravenous drip infusion. The changing patterns of the tissue concentrations were similar to those in the serum. The penetration of AC-1370 into intrapelvic dead space exudate was good. The level reached a peak of 35 micrograms/ml at 2 approximately 4 hours after an intravenous drip infusion with 1 g and 3.7 micrograms/ml after 12 hours. AC-1370 was effective in 20 out of 21 cases (95.2%) with gynecoobstetrical infections such as intrauterine, intrapelvic infection and mammitis, administered with 1 approximately 2 g twice a day. Few side effects were observed.