Following an intravenous injection of ceftazidime (CAZ) 1 g, the ratio of transfer of the drug into a fetus was 59.9%, and umbilical serum concentrations of the drug reached the peak of 18.2 micrograms/ml at 1.5 hours, and were slightly higher than maternal serum concentrations at 2.93 hours and after, with half-life of 1.37 hours, the same as in maternal serum. Following an intravenous injection of CAZ 1 g, concentrations of CAZ in mother's milk at 2 hours after injection were 1.16 micrograms/ml on the 4th day of the treatment of CAZ, and 0.86 micrograms/ml on the 7th day. The CAZ was administered to cases of premature rupture of membrane. The prophylactic efficacy against puerperal infections in mothers was 92%, and that against fetal infections in neonates was 96.7%. The CAZ was also administered after cesarean section, and the prophylactic efficacy against postoperative infections was 93.3%. Neither subjective/objective adverse effects nor abnormal laboratory findings for which CAZ was suspected were observed in any mothers or neonates. From the above results demonstrating satisfactory maternal transfer into fetuses and the high degree of safety in fetuses and neonates, as well as its high antibacterial activity, CAZ is considered to be a useful drug for the treatment of perinatal infections.