Fundamental studies and clinical evaluation of CS-1170 were carried out in the field of pediatrics, and the following results were obtained: 1) A high serum concentration of the drug was observed by 30 minutes after the commencement of intravenous drip infusion of 20 and 30 mg/kg, with the peak appearing at the end of the infusion. Serum level of 10.0 micrograms/ml or more was observed even 2 hours after the completion of the drip infusion. 2) The peak of serum concentration appeared at 30 minutes after intravenous injection of 20 mg/kg, and the blood level 4 hours after the injection was 4.3 micrograms/ml or more. 3) Excretion of the drug into the urine by 6 hours after intravenous drip infusion or one-shot injection was 60% or more on the average, with the major portion of the drug in the active state excreted by 4 hours after the administration. 4) Twenty-five children with acute infections (5 types of diseases) were treated with CS-1170 mainly by intravenous drip infusion, and the following clinical results were obtained: The overall clinical effective rate of 96.0% was obtained with the daily dosage of CS-1170 ranging mostly from 50 to 80 mg/kg in the total 25 cases including 7 cases of acute bronchitis (100%), 13 cases of bronchopneumonia (92.3%), 3 cases of acute urinary tract infections (100%), a case each of staphylococal exanthema and lymphadenitis in the neck (100%). 5) Thorough analyses of the liver and kidney functions and the hematological features at the time of, and about 10 days after the administration of CS-1170 in each case so far revealed no abnormality. The drug did not affect the site of injection or the whole body.