Cefprozil (CFPZ, BMY-28100) granules was administered to a group of pediatric patients. The new oral cephalosporin, CFPZ, was evaluated clinically in 42 pediatric patients, and a pharmacokinetic study was performed in 6 patients. Serum and urinary concentrations of CFPZ were determined in 6 patients who were given single dose of 7.5 or 15.0 mg/kg. Serum concentrations were determined at 1, 2, 3, 4 and 6 hours after dosing. Urinary concentrations were measured for periods of 0-6 hours after dosing. With oral administrations of 7.5 mg/kg and 15.0 mg/kg, peak serum concentrations were 2.13 micrograms/ml and 6.22 micrograms/ml, respectively, at 2 hours, and biological half-lives were 1.06 hours and 1.36 hours, respectively. Urinary recovery rates were 44.8% and 56.1%. The clinical evaluation was conducted in 41 patients including 16 patients with acute tonsillitis, 8 patients with lacunar tonsillitis, 4 patients with scarlet fever, 3 patients with acute bronchitis, 1 patient each with pertussis, furuncle, impetigo and lymphadenitis, and 6 patients with urinary tract infections. The ages of the patients were 10 month to 11 years 1 month, and they were treated with CFPZ at doses ranging 9.0-45.0 mg/kg daily for 3-14 days, the overall clinical efficacy rate was 92.7%. An eradication rate of 79.2% was achieved for 28 strains of 8 species identified in the patients. No side effects were observed. Abnormal laboratory test results obtained were eosinophilia in 2 patients.