Fundamental and clinical studies of ceftazidime (CAZ) were performed in pediatric surgery. The results obtained were summarized below. Serum and urinary levels of CAZ were measured in 5 patients following injection (CAZ: 10 or 20 mg/kg, intravenous bolus injection). Highest levels in serum were observed within 30 minutes, 30.4 micrograms/ml and 49.5-62.9 micrograms/ml with 10 mg/kg and 20 mg/kg doses, respectively. Then serum levels of CAZ decreased gradually except in 1 case with a metabolic disease, and serum half-lives (T 1/2) were 1.19-1.88 hours for the high doses. The highest levels in urine were observed in 0-2 hours, and the urinary recovery rate was 59-100%. The bile levels were also measured in 3 patients who underwent radical operations of congenital biliary atresia (CBA). Highest levels of CAZ in bile, 4.47-9.66 micrograms/ml, were noted in 0-2 or 2-4 hours following injection. Recovery rates for 8 hours were 0.11, 0.17 and 0.20% for the 3 patients. The CAZ was administrated to 7 patients for prophylaxis of the postoperative infection (5 cases) or to treat ascending cholangitis in CBA (2 cases). Clinical results were good in 4, fair in 1, poor in 1 and unknown in 1. No clinical and laboratory side effect due to the administration of CAZ was observed. It is concluded that CAZ is a safe and effective antibiotic in pediatric surgery.