CS-1170 was tried in children with various infections, and the following results were obtained. Some studies on the drug's pharmacokinetics were also made, and the results were as shown below: 1. The time course of serum concentration following one-shot intravenous injections of 30 mg/kg in 8 patients aged between 3 and 13 was studied. The results were: 53.4 microgram/ml, 23.4 microgram/ml, 6.6 microgram/ml, 1.8 microgram/ml and 0.5 microgram/ml at 30 minutes, 1 hour, 2 hours, 4 hours and 6 hours after the drug administration, respectively. Urinary recovery rate was 36% to 69.8% by 2 hours after, 10.9% to 70% by 2 to 4 hours after, 0.6% to 5.4% by 4 to 6 hours after the administration, and by 8 hours after the injection 91.3% of the drug was excreted in the urine. 2. Of 13 cases including 8 cases of bronchopneumonia, 2 cases of urinary tract infections, a case each of suppuration in the neck, lymphadenitis and pyothorax, CS-1170 was found to be effective in 10 cases (83.3%), while effectiveness of the drug was undeterminable in one case. 3. No remarkable side effect including allergic symptom such as eruption was observed, though transient elevation of GOT and GPT was noted in one case.