Aztreonam (SQ 26,776, AZT), a new monobactam antibiotic, was fundamentally and clinically studied with the following results. Uterine and adnexal concentrations of AZT after intravenous injection of 1 g were highest 3 hours after administration in the ranges of between 18.6-23.4 micrograms/g 16.5-28.2 micrograms/g, respectively, and and rapidly decreased thereafter. Penetration of AZT into the pelvic dead space exudate was quickly recognized after intravenous injection of 1 g and its concentration 30 minutes after administration was 14.08 +/- 7.08 micrograms/ml and highest (22.35 +/- 5.85 micrograms/ml) 2 hours after administration. It gradually decreased to 8.50 +/- 2.07 micrograms/ml 6 hours after administration. Clinical effect was studied by administering 1-3 g of AZT twice a day for 3-16 days by intravenous drip infusion for 18 patients with various infections in the field of obstetrics and gynecology. Efficacy of AZT for 9 genital infection cases were excellent for 4 cases, good for 4 cases and poor for 1 case, with an overall efficacy rate of 88.9%. For 2 UTI cases, it was excellent for one case and good for the other, and for 4 pelvioperitonitis cases, excellent for 3 cases and good for 1 case. For 2 inflammation cases of the pelvic dead space, efficacy of AZT was excellent for both of them. With regard to side effect, there was only one rash case experienced. It was considered from the above results that AZT is sufficiently useful for the infections in the field of obstetrics and gynecology and also useful for various gynecologic surgery cases.