Two-hundred nine patients with symptoms of acute urinary tract infection and pyuria were randomized to 400 mg of administered norfloxacin twice daily for three days, or 800 mg of sulfamethoxazole and 160 mg of trimethoprim administered twice daily for ten days. Therapeutic outcome was assessed five to nine days and four to six weeks after treatment. The cure rates were 71/74 (96%) with norfloxacin and 81/81 (100%) with sulfamethoxazole and trimethoprim five to nine days after treatment. Only seven patients had a recurrence at the second follow-up visit; four in the norfloxacin group and three in the sulfamethoxazole and trimethoprim group. No isolates were resistant to norfloxacin, but three Escherichia coli were resistant to sulfamethoxazole and trimethoprim. Fifteen patients in each group reported a side effect during treatment. Two patients in the norfloxacin group and four patients in the sulfamethoxazole and trimethoprim group discontinued therapy due to an adverse effect. In this multicenter study, a three-day course of norfloxacin was as effective and safe as a ten-day regimen of sulfamethoxazole and trimethoprim in the treatment of acute uncomplicated urinary tract infections.