Fundamental and clinical studies on cefminox (CMNX, MT-141), a new cephamycin antibiotic, were carried out and the following results were obtained. When CMNX was administered at a dose of 1 g by intravenous drip infusion taking 1 hour, the serum concentrations as high as 20 micrograms/ml and 21 micrograms/ml were detected even at 4 hours after administration for the uterine artery and elbow vein, respectively. From these results, CMNX was supposed to maintain in vivo concentrations high enough to inhibit 80 to 100% of the growth of bacteria such as S. aureus, E. coli, Klebsiella, Proteus and anaerobic bacteria, B. fragilis, which are the commonest clinical isolates in the field of obstetrics and gynecology. Clinically, in 7 cases of female genital infections (4 cases of parametritis, 1 case of intrauterine infection, 1 case of pyometra and 1 case of pelveoperitonitis), CMNX was administered at a daily dosage of 2 g in 2 divided doses as intravenous drip infusions taking 90 minutes each. The clinical results were excellent in 1 case, good in 3 cases and poor in 3 cases, with an efficacy rate of 57.1%. In 6 out of these 7 cases progressive carcinoma was present as the underlying disease. No side effects nor abnormalities in laboratory findings were observed in any of the 7 cases. These results suggest that CMNX is effective in the treatment of obstetrical and gynecological infections.