Basic and clinical studies were made on ceftazidime (CAZ) in pediatric field, and the following results were obtained. The antibacterial activity of CAZ against clinically isolated and maintained strains was examined. CAZ was unequivocally more active than CEZ and CMZ against Gram-negative rods, with MIC distribution similar to that of CTX, except for that for P. aeruginosa. The MIC of CAZ was lower than that of CTX for P. aeruginosa. Compared with the MICs of CEZ, CMZ and CTX, CAZ showed slightly higher MICs for Gram-positive bacteria. The blood concentrations of CAZ, at 0.25, 0.5, 1, 2, 4 and 6 hours after a one shot intravenous injection of 10 mg/kg of CAZ were 64.9, 36.9, 28.3, 14.7, 4.92 and 2.42 micrograms/ml, respectively, with the half-life of 1.27 hours. The blood concentrations of CAZ, at 0.25, 0.5, 1, 2, 4 and 6 hours after a 1-hour drip infusion of 10 mg/kg of CAZ were 16.6, 24.5, 41.4, 17.1, 5.38 and 2.62 micrograms/ml, respectively, with the half-life of 1.28 hours. The blood concentrations of CAZ, at 0.25, 0.5, 1, 2, 4 and 6 hours after a one shot intravenous injection of 20 mg/kg of CAZ were 73.1, 60.8, 39.3, 17.3, 8.23 and 4.45 micrograms/ml, respectively, with the half-life of 1.42 hours. The blood concentrations of CAZ, at 0.5, 1, 2, 4 and 6 hours after a 1-hour drip infusion of 20 mg/kg of CAZ were 55.1, 69.0, 32.1, 11.4 and 4.56 micrograms/ml, respectively, with the half-life of 1.27 hours. Urinary recovery rate of CAZ during the first 6 hours after a one shot intravenous injection of 10 mg/kg of CAZ was 86.7%. CAZ was administered to 17 children with infections, and the clinical response was excellent or good in 94%. CAZ was bacteriologically effective in 14 patients, all bacteria having been eradicated in them. The bacteria were E. coli in 10 patients, H. influenzae in 2, P. aeruginosa in 1 and S. pneumoniae in 1. As for side effects, slight elevation in GOT was observed in 1 case and eosinophilia, in another case.