Cefminox (CMNX, MT-141), a new cephamycin antibiotic, was studied in the field of obstetrics and gynecology, and the following results were obtained. The absorption and the penetration of CMNX into pelvic dead space exudate were good. The mean peak serum level after single intravenous injection was 190.8 micrograms/ml. The level in pelvic dead space exudate reached a peak of 36.6 micrograms/ml 4 hours after an intravenous injection of 1 g and 6.5 micrograms/ml after 12 hours, thus the level over MIC against main pathogenic organisms was maintained for a long time. CMNX was administered against gyneco-obstetrical infections such as intrauterine, intrapelvic, adnexal infections and postoperative wound infections with daily dose of 2 g and was effective in 11 cases out of 12 cases (91.7%), and 81.8% of bacteriological effect was obtained. No side effect was observed. From the above results the usefulness of CMNX in the field of obstetrics and gynecology was suggested.