A new sulfonamide, sulfacytine, was compared in a double-blind study with sulfisoxazole for the treatment of acute uncomplicated urinary tract infection in 98 outpatients. Patients received either 4 gm. sulfisoxazole or 1 gm. sulfacytine daily for 10 days. Evaluation was made of the bacteriologic and clinical success within the period of treatment and at some point after treatment. Bacteriologic success, or reduction of urine bacterial count from 100,000 or more micro-organisms per ml. to 1,000 or less, was observed in 95 to 100 per cent of the patients in each group during treatment as well as at the post-treatment evaluation. Clinical success, or the abolition of dysuria and frequency of urination and the reduction of pyuria to less than 10 white blood cells per high power field, was observed in 75 to 85 per cent of the patients. Adverse reactions were rare, involving 1 instance each of headache, nausea and hematuria in the sulfisoxazole group, and drug attributability was only possibly established. Mild laboratory abnormalities occurred in each group, 2 cases each of decreased white blood count and 1 instance of a lowered hemoglobin in a patient in the sulfacytine group. The results of our study seem to indicate that sulfacytine is an effective drug for the treatment of acute uncomplicated urinary tract infections.