Fundamental and clinical effects of cefprozil (CFPZ, BMY-28100) granules, a new oral cephalosporin antibiotic, in pediatric field were investigated. The result obtained were summarized as follows. 1. CFPZ (10% granules) was given to 1 child in a single dose of 7.5 mg/kg. The peak serum concentration of CFPZ was 4.51 micrograms/ml at 2 hours after administration. Half-life and AUC values were 0.98 hour and 20.7 micrograms.hr/ml. The mean peak urinary concentrations of CFPZ and 6 hours recovery rates were over 200 micrograms/ml at 2-6 hours and 27.6%, respectively. 2. Clinical efficacy of CFPZ was investigated in a total of 41 children, including 14 with upper respiratory tract infections, 6 with acute bronchitis and pneumonia, 2 with acute otitis media, 3 with skin and soft tissue infections and 16 with urinary tract infections. The clinical efficacy rate was 95.1%. The bacteriological eradication rate was 84.6%. 3. Two patients showed abnormal laboratory test results. One had elevations of both GOT and GPT, and another had eosinophilia which were attributed to this antibiotic as side effects.