We have investigated bioavailability, clinical efficacy, side effect and antimicrobial activity of norfloxacin (NFLX) to evaluate the efficacy and safety in the pediatric field. Results are summarized as follows 1. After oral administration of 100 mg, Tmax was 2 hours and T 1/2 were 4.2 and 2.6 hours in 2 cases. 2. In 10 cases of urinary tract infection (UTI) and 4 cases of intestinal tract infection (ITI), clinical efficacy rate was 100% (14/14). 3. In UTI, causative bacteria were all eradicated. In ITI, 1 case with Campylobacter jejuni remained unchanged. Overall eradication rate was 92.9% (13/14). 4. Antimicrobial activities to clinically isolated organisms such as Gram-negative rods or Staphylococcus aureus, MIC of NFLX was clearly superior to those of cefaclor, amoxicillin, nalidixic acid, fosfomycin and erythromycin. 5. Side effect of dipsia was observed in 1 case and eosinophilia was found in 1 case. But these reactions were mild and we were able to continue the administration of the drug. The above results suggest that NFLX is a useful and safe drug for the therapy of UTI and ITI in the pediatric field.