Fundamental and clinical studies on cefpimizole (AC-1370), a new cephem antibiotic, were performed and the following results were obtained: Concentration of AC-1370 was examined in serum, internal genital organs and retroperitoneal fluid after single intravenous administration of 2.0 g dose. The venous serum level of AC-1370 was 243 micrograms/ml at 30 minutes after the administration. The sufficient transfer of AC-1370 to internal genital organs and retroperitoneal fluid was recognized. In clinical trial, AC-1370 was given to 10 cases with obstetrical and gynecological infections. The efficacy was evaluated as good in 8 cases and poor in 2 cases. No side effects were observed in any of the cases treated with AC-1370.