Norfloxacin (NFLX) tablets with a potency of 50 mg/tablet or 100 mg/tablet were administered at doses of 1 to 4 tablets (1.5 to 6.1 mg/kg) orally 30 minutes before meals to 12 children with ages ranging from 8 years 9 months to 12 years 5 months, and serum/urinary NFLX levels and urinary recovery rates were determined. The drug sensitivity tests for NFLX and 10 other drugs were conducted against 128 strains of Shigella sonnei (10(6) CFU/ml) which had been isolated from pediatric patients with bacillary dysentery. In order to evaluate clinical and bacteriological effects of NFLX and its safety in the pediatric field, NFLX 50 mg tablets were administered t.i.d. (mean 8.3 mg/kg) for 5 days to 42 pediatric patients with bacillary dysentery. Similarly, this drug was administered in b.i.d. or t.i.d. (mean 6.7 mg/kg) for 4 days to 4 pediatric patients with urinary tract infections. The following results were obtained: 1. According to the dosage, the subjects were divided into 3 groups with dose levels 1.5-2.8 mg/kg, 3.1-4.7 mg/kg and 5.2-6.1 mg/kg. These groups had 5, 2 and 5 subjects, respectively. Mean serum drug concentrations for the 3 dosage groups were at peak levels of 0.27, 0.64 and 1.51 micrograms/ml at 4, 2 and 1 hour(s) after administration, respectively. Pharmacokinetic parameters for these dosage groups were as follows: Tmax values were 3.0, 3.0 and 1.2 hours; Cmax values were 0.32, 0.78 and 1.56 micrograms/ml; serum half-lives were 2.2, 2.4 and 2.3 hours; and AUCs were 1.65, 3.98 and 6.06 micrograms.hr/ml, respectively. Thus, dose-dependent responses were observed among the 3 dosage groups. 2. Mean peak urinary drug concentrations for the 3 dosage groups were 45.8, 109.2 and 215.1 micrograms/ml, respectively, and the peaks appeared 2-4 hours after administration. Mean recovery rates up to 8 hours after administration were 18.3%, 24.5% and 28.7%, respectively for the 3 dosages. 3. In a drug sensitivity test against 128 strains of S. sonnei, the most frequent MIC value of NFLX was 0.78 micrograms/ml against 65 strains, followed by 0.39 micrograms/ml for 56 strains. Together, these strains accounted for 94.5% of the strains tested. No resistant strain to this drug was observed and the antibacterial activity of this drug was second only to colistin, similar to that of ofloxacin, better than those of enoxacin and seven other drugs. 4. Clinical efficacy rate of NFLX against bacillary dysentery was 95.2% in 21 cases in which the evaluation was possible.(ABSTRACT TRUNCATED AT 400 WORDS)