Fundamental and clinical studies on gynecological use of aztreonam (AZT), a new monobactam, were performed with following results. Following the intravenous administration of 1 g dose of AZT, the transfer of AZT to pelvic dead space exudate was good, in which the concentration of that was 14.9 micrograms/ml (2 hours), 15.3 micrograms/ml (3 hours) after injection. The transfer of AZT to serum of umbilical cord and amniotic fluid was excellent. In a clinical trial, AZT was given to 5 patients with obstetric and gynecological infections. The clinical efficacy was evaluated as excellent in 1 case and good in the other 4 cases. No adverse effects were observed in any of the patients treated with AZT.