Bacteriological and clinical studies on norfloxacin (NFLX) were carried out in the field of pediatrics, and the results obtained are summarized as follows: 1. The MICs of NFLX against clinically isolated organisms were determined to compare with MICs of nalidixic acid, amoxicillin, cefaclor, erythromycin and fosfomycin. NFLX had low MICs against both Gram-positive and Gram-negative bacteria and, particularly, showed higher antimicrobial activity to Escherichia coli, Salmonella sp., Klebsiella pneumoniae, Pseudomonas aeruginosa, Haemophilus influenzae and Campylobacter jejuni than any other drugs tested. 2. Seventeen pediatric patients (11 cases of enteritis, 4 cases of urinary tract infections, 1 case of tonsillitis and 1 case of pyoderma) were treated orally with NFLX in daily doses ranging from 3.1 to 16.7 mg/kg t.i.d. for 6-14 days. Rates of clinical effectiveness and bacterial elimination were 94.1% and 58.8%, respectively. 3. None of the treated children showed clinical symptoms indicating the occurrence of side effects nor abnormal laboratory findings except 1 patient with eosinophilia. These results indicate the usefulness of NFLX in the treatment of bacterial infections in the pediatric field.