We studied pharmacokinetics and clinical effects of 5% and 10% fine granules of cefdinir (FK 482, CFDN), a new oral cephalosporin, in the pediatric field and the following results were obtained. 1. Pharmacokinetics (blood concentration and urinary excretion) Pharmacokinetics of CFDN in 163 children was investigated. Cmax and T 1/2 were 0.92 +/- 0.45 micrograms/ml and 1.95 +/- 1.06 hours, respectively, in the fasting state, and were 0.63 +/- 0.29 micrograms/ml and 2.26 +/- 0.65 hours, respectively, in the non-fasting state, at a dose level of 3 mg (potency)/kg. At a dose level of 6 mg (potency)/kg, Cmax and T 1/2 were 1.29 +/- 0.49 micrograms/ml and 2.11 +/- 1.85 hours, respectively, in the fasting state and were 1.28 +/- 0.48 micrograms/ml and 2.01 +/- 0.84 hours, respectively, in the non-fasting state. Data of Cmax and AUC showed that blood concentration of the drug depended on dose levels. Urinary recovery rates in the first 8 hours were 20.5 +/- 8.8% in the fasting state and 14.8 +/- 5.9% in the non-fasting at a dose level of 3 mg (potency)/kg and 16.5 +/- 6.7% and 17.8 +/- 2.4%, respectively, at 6 mg (potency)/kg. 2. Clinical effects Clinical effects of CFDN on various infections were studied in 612 children who were treated with 5% fine granules of CFDN (5% granule group) and in 208 with 10% fine granules of CFDN (10% granule group). CFDN granules were administered mainly at daily doses of 9.0-18.0 mg (potency)/kg in 3 divided portions. Clinical efficacy rates in 428 children of the 5% granule group and in 159 of the 10% granule group from whom causative bacteria were isolated, were 94.9% and 96.2%, respectively. The clinical efficacy rates for patients who were responsive to previous antibiotic therapy were 91.2% in the 5% granule group and 100% in the 10% granule group. Bacteriological eradication rate was 82.1% for 491 strains in the 5% granule group, and was 84.0% for 175 strains in the 10% granule group. The incidences of side effects were 3.9% (24/608) in the 5% fine granule group and 5.8% (12/206) in the 10% granule group. All of the side effects were slight gastrointestinal disorders, and no serious side effects were found. As for clinical laboratory test results, slight elevations of eosinophile, platelet or transaminase were observed. Based on the above results, it is considered that the appropriate dose levels of CFDN for pediatric infections ranged from 9.0 to 18.0 mg (potency)/kg a day, divided into 3 portions.