The fundamental and clinical studies of ceftizoxime suppository (CZX-S) in the field of pediatrics were made, with the following results. The serum concentration of CZX in the CZX-S 250 mg-administered group peaked 6.00-22.5 micrograms/ml during the period of 15 minutes to 1-hour after dosing, and gradually declined thereafter. The half-life was 1.37-3.81 hours. In the CZX-S 125 mg-administered group, the serum concentration peaked 2.25-21.0 micrograms/ml at 15-30 minutes after dosing and decreased with time. The half-life was 0.95--1.84 hours. The 6-hour urinary recovery rate of CZX in the CZX-S 250 mg group was 22.0-47.5%. The 6-hour urinary recovery rate in the CZX-S 125 mg group was 17.2-25.3%. CZX-S was given 12-73 mg/kg/day (divided into 1-3 times) to 7 children with respiratory tract infection etc. who were considered to respond well to the drug. The clinical effectiveness rate was 100% inclusive of "excellent" and "good". The side effect of pain on insertion was encountered in 1 child.