The study was undertaken to compare the safety and efficacy of twice-daily ciprofloxacin for 3 days with standard 7 day therapy with either co-trimoxazole or nitrofurantoin in the treatment of women with acute, uncomplicated urinary tract infections (UTI). This multicentre, prospective, randomized, double-blind trial compared oral ciprofloxacin (100 mg bd) for 3 days with co-trimoxazole (160/800 mg bd) or nitrofurantoin (100 mg bd) for 7 days. Bacteriological and clinical evaluations were performed at study entry, during therapy and 4-10 days and 4-6 weeks after the completion of therapy. The primary efficacy parameter was eradication of the causative organism 4-10 days following treatment. Of 713 women enrolled and evaluable for safety, 521 were evaluable for efficacy (168 ciprofloxacin, 174 co-trimoxazole, 179 nitrofurantoin). Escherichia coli (83%) was the most frequently isolated pathogen in all treatment groups. Bacteriological eradication was reported in 88% of ciprofloxacin patients, 93% of co-trimoxazole patients and 86% of nitrofurantoin patients. At the 4-6 week follow-up, ciprofloxacin had statistically significantly higher eradication rates (91%) than co-trimoxazole (79%; 95% confidence limit (CL) = -20.6%, -3.9%) and nitrofurantoin (82%; 95% CL = -17.1%, -0.9%). Clinical resolution 4-10 days after therapy and at the 4-6 week follow-up was similar among the three treatment groups. The overall incidence of treatment-emergent adverse events was not significantly different (P = 0.093) among the three drug regimens, although co-trimoxazole was associated with a greater number of adverse events than ciprofloxacin (P < or = 0.05). Ciprofloxacin also caused fewer episodes of nausea than either of the other agents (P < or = 0.01).