In treating acute infections of the urinary tract, a sulfonamide drug is recommended as the first choice; if the program here outlined fails, the reason is likely to be either specific bacterial resistance or the presence of structural abnormalities. In treating chronic infections broad-spectrum antibiotics are suggested. The authors review previously published observations on 75 patients treated with kanamycin. The original organism was eradicated in about 60% of this group, but other organisms emerged after or even before the treatment was ended in about 30%. The experience of the authors indicated that underlying urologic abnormalities should be searched for, that sensitivity tests are of value in choosing the antibiotic best suited to the infecting organism, and that the possible development of resistance to the antibiotic on the part of the organism must be kept in mind.