Bacteriological, pharmacokinetic and clinical studies on cefpirome (CPR, HR 810), a new cephem antibiotic, were carried out in the field of pediatrics. The results obtained are summarized below. 1. Antibacterial activities of CPR against clinically isolated strains of Staphylococcus aureus, Streptococcus pneumoniae, Streptococcus pyogenes, Streptococcus agalactiae, Escherichia coli, Klebsiella pneumoniae, Haemophilus influenzae and Haemophilus parainfluenzae were superior to those of ceftazidime. 2. Plasma concentrations and urinary excretion rates after intravenous bolus injection of CPR at doses of 10, 20 and 40 mg/kg for 5 minutes in 2 cases each were determined. Mean peak plasma concentrations of CPR at these dose levels were 33.9, 62.9 and 96.0 micrograms/ml at 15 minutes with plasma half-lives of 1.58, 1.69, and 2.13 hours, respectively. Mean cumulative urinary excretion rates in the first 8 hours after administration were 51.2, 78.0 and 74.9%, respectively. 3. Ten patients with bacterial infections (pneumonia 5 cases, urinary tract infection 5 cases) were treated with CPR at a daily dose of 16-79 mg/kg/day. The overall clinical efficacy and bacteriological eradication rates were both 100%. 4. No adverse reactions were observed except in 1 case of mild pain in blood vessels. Abnormal laboratory test results were also mild, slight elevation of GOT, GPT and thrombocytosis in 1 case and eosinophilia in 1 case.