The Pharmacokinetics and clinical effectiveness of cefdinir (CFDN, FK482) were examined in pediatric patients. The results are summarized as follows. 1. Plasma concentrations and urinary excretions of CFDN after administration of 5% fine granules were investigated on 4 children at a dose level of 6 mg/kg. Average plasma concentrations peaked at 4 hours after administration at 0.99 micrograms/ml with a half-life of 2.12 hours. The first 24-hour urinary recovery rates of CFDN in 3 children averaged 22.0%. 2. CFDN was given to 24 children (11 with pharyngitis, 3 with tonsillitis, 8 with scarlet fever, 1 with urinary tract infection and 1 with enteritis due to Salmonella); 15 were treated with 5% fine granules and 9 with 10% fine granules at daily doses of about 10 mg/kg in 2 to 3 divided portions. Clinical effects were excellent in 16, good in 7 and not evaluable in 1, with an overall efficacy rate of 100%. 3. Identified causative organisms were 12 strains of Streptococcus pyogenes, 4 of Haemophilus influenzae, 5 of Haemophilus parainfluenzae, 1 of Escherichia coli, and 1 of Salmonella. Bacteriological effects were rated as "eradicated" for 19 strains, "unchanged" for 4 with an eradication rate of 82.6%. 4. No side effects were observed. As for abnormal laboratory test results, a transient decrease of white blood cells was observed in 1 patient. 5. The CFDN fine granule preparations were preferably accepted by the children. 6. The fine granular preparations of CFDN, a new oral antibiotic, were useful for the treatment of bacterial infections in pediatrics.