Cefuzonam (CZON), a new cephem antibiotic agent, was studied in terms of its pharmacokinetics and clinical efficacy in the field of obstetrics and gynecology, and the results were summarized as follows. 1. The absorption and the tissue penetration of CZON into intrapelvic genital organs were good. The peak serum level in uterine artery after an intravenous drip infusion of 1.0 g was 49.0 micrograms/ml, and the highest peak level of 23.0 micrograms/g in tissues was obtained. After drip infusion of 2.0 g, the peak serum level in uterine artery was 137 micrograms/ml and the highest peak tissue concentration was 54.6 micrograms/g. Tissue concentrations of the drug changed in a similar pattern to serum levels and a dose-dependent response was recognized. 2. The penetration of CZON into intrapelvic dead space exudate was good. The level reached a peak of 8.17 micrograms/ml 4 hours after and intravenous drip infusion of 1.0 g and diminished slowly. 3. The clinical efficacy of CZON at a daily dose of 2 g was evaluated in 21 cases of obstetrics and gynecologic infections. The efficacy rate was 85.7% (18/21 cases). Bacteriologically, the eradication rate obtained was 93.3%. No side effects or abnormal laboratory values were observed.