The peak levels of serum ceftizoxime (CZX) after a single rectal administration of CZX-S at doses of 125 and 250 mg in 157 pediatric patients were occurred at 21 approximately 25 minutes in pediatric patients aged less than 1 year and over than 7 years, at 16-20 minutes in 1-3 years patients, at more than 26 minutes in 4-6 years patients. They were 9.45, 9.58, 11.71, 12.43 mcg/ml, respectively. The mean highest levels of serum CZX were 8.56, 10.66, 12.50 mcg/ml after the administration of CZX-S as less than 10.0, 10.1-15.0, 15.1-20.0 mg/kg dose respectively, all of which were occurred at 21-25 25 minutes. A close dose response was observed. The pain of insertion was not observed in any cases. The discharge of melted suppository or defecation after administration was observed in 15.2% of total 184 cases, which was noticed more frequently in the lower aged children. There was no influence by dose. Clinical effects of CZX-S were studied in 72 pediatric patients with various infections. CZX-S was administered rectally at the mean daily dose of 41.0 mg/kg divided into 3 or 4 times for 6 days. Clinical responses were excellent in 46 cases, good in 24 cases, fair in 2 cases. The efficacy rate was 97.2%. Regarding side effects, the pain of insertion was noted in 2 cases (2.8%), diarrhea in 6 cases (8.3%), the elevation of eosinophil in 1 case (1.7%). Bacteriologically, 23 strains (92.0%) out of 25 strains isolated from the patients were eradicated.