The authors have carried out the pharmacokinetics and clinical studies of CS-1170. The results were as follows; CS-1170 was given by drip infusion for 1 hour dose of 20 mg per kg body weight to 3 children. The maximum blood level was reached at one hour after drip infusion. This blood levels were 38 micrograms/ml, 68 micrograms/ml and 86 micrograms/ml, respectively, (mean 64 micrograms/ml), and level at 2 hours, 11.5 micrograms/ml, 9.4 micrograms/ml, 16 micrograms/ml respectively, (mean 12.3 micrograms/ml), the blood level at 6 hours was not determined. The urinary excretion rates were 94.8 approximately 96.8% up to 6 hours after drip infusion dose of 20 mg per kg body weight. CS-1170 was effective in 7 of 8 cases with pediatric bacterial infections. An ineffective case was a pneumonia due to Serratia marcescens. No side effect was observed except for 2 cases with diarrhea and one case with elevation of GOT and GPT.