Ceftazidime ( CAZ ), a newly-developed parenteral cephem antibiotic, was administered to 8 children; by one shot intravenous (i.v.) injection in the doses of 20 and 40 mg/kg each to 2 children, and by 30 minutes' i.v. drip infusion in the doses of 10 and 20 mg/kg each to 2 children, and the serum levels, urinary levels and recovery rates were determined. CAZ was also administered to 2 patients with purulent meningitis, one complicated with subdural abscess and the other with bacteremia, in the doses of 19.2 and 50.7 mg/kg, respectively, by one shot i.v. injection, and the CSF level of CAZ was determined. In addition, CAZ was administered to 2 children with acute bronchitis, 1 with chronic bronchitis, 37 with pneumonia, 3 with pleuropneumonia, 1 each for purulent meningitis, purulent meningitis accompanied with subdural abscess and purulent meningitis with bacteremia, 5 with urinary tract infections and 3 with purulent lymphadenitis (total 54 children), in the mean dose of 85.8 mg/kg/day mostly in 4 divided doses by one shot i.v. injection for 9 days on the average, and clinical effectiveness and bacteriological response were evaluated in these cases, and adverse events and abnormal laboratory findings were examined in the 66 cases which included 12 drop-out cases. 1. After the administration of CAZ to 4 children; 20 and 40 mg/kg each to 2 children, by one shot i.v. injection, the mean serum levels got to the peak of 115.8 and 199.5 mcg/ml, respectively, at 5 minutes. The results were good, showing dose response. The mean half-lives were 1.48 and 1.37 hours, respectively. After the administration of 10 and 20 mg/kg of CAZ each to 2 children by 30 minutes' i.v. drip infusion, the mean serum levels got to the peak of 58.5 and 80.0 mcg/ml, respectively, on completion of the administration, showing dose response. The mean half-lives were 1.06 hours in the former 2 cases, and 1.38 and 3.26 hours, respectively, in the latter 2 cases. The reason for the prolongation observed in 1 case was not clear. 2. In the above mentioned each 2 cases receiving one i.v. injection, the mean urinary levels got to the peak of 4,240 and 4,445 mcg/ml, respectively, at 0-2 hours after the administration , and the urinary recovery rates during the first 6 hours were high, 95.7% and 99.5%, respectively.(ABSTRACT TRUNCATED AT 400 WORDS)