A new sulfonamide, sulfacytine, was compared in a double-blind study with sulfisoxazole in 132 patients with uncomplicated urinary tract infections. At the doses used, 1Gm. per day of sulfacytine of 4 Gm. per day sulfisoxazole, bacteriologic success (decrease of pathogenic organisms from greater than or equal to 100,000 to less than or equal to 1,000 per milliliter of urine) was demonstrated in approximately 90 per cent of the patients. Clinical success (subsidence of the symptoms, frequency of urination, and dysuria, and reduction of pyuria from greater than or equal to 10 to less than 10 white blood cells per high-power field) occurred in 85 to 90 per cent. Six patients in the sulfacytine group and 9 in the sulfisoxazole group reported adverse experiences. Drug was discontinued or administration interrupted because of adverse experiences in 4 sulfacytine patients and 6 sulfisoxazole patients. Laboratory values generally remained normal, but 1 patient in each medication group had decreases in white blood cells that might have been attributable to drug. On the basis of this study sulfacytine appears to be an effective drug for the treatment of uncomplicated urinary tract infections.