Cefpirome (CPR, HR 810), a new parenteral cephalosporin antibiotic, was studied for its pharmacokinetics, bacteriological and clinical effects in the field of pediatrics. 1. CPR was very active against Staphylococcus aureus, Staphylococcus epidermidis, Coagulase-negative staphylococci, Streptococcus pneumoniae among Gram-positive cocci. Antibacterial activities of CPR were also strong against Branhamella catarrhalis, Haemophilus influenzae, Escherichia coli, Salmonella sp., Klebsiella oxytoca, Enterobacter cloacae, Pseudomonas aeruginosa among Gram-negative rods. 2. The plasma concentration 15 minutes after a bolus intravenous injection of 20 mg/kg was 80.4 micrograms/ml, and the T 1/2 (beta) was 1.03 hours. Plasma concentrations after intravenous drip infusion over 30 minutes of 20 mg/kg and 25 mg/kg were 48.3 and 117 micrograms/ml at the end of infusion, and T 1/2 (beta) for these dosage were 1.14 and 1.45 hours. 3. The urinary recovery rates over 6 hours after administration were 45.2-63.9% for CPR. 4. Clinical efficacies of CPR were excellent in 31 patients and good in 30 patients with an efficacy rate of 98.4%. In bacteriological examinations, causative organisms were eradicated with an eradication rate of 95.7%. 5. As side effects, diarrhea was observed in 5 patients and loose stool in 1 patient with an incidence of 8.2%. Abnormal values were found in some patients in clinical laboratory tests for eosinophilia, thrombocytosis and an elevation of GOT, GPT and triglyceride. These findings indicate that CPR will be useful against bacterial infections in pediatrics.