The efficacy and safety of a 3-day regimen of sparfloxacin were compared with those of a 3-day regimen of ofloxacin for the treatment of community-acquired acute uncomplicated urinary tract infections. Four hundred nineteen women were enrolled in a randomized, open-label, observer-blinded, multicenter study; 204 received sparfloxacin as a 400-mg loading dose on the first day and 200 mg once daily thereafter, and 215 received ofloxacin as 200 mg twice daily. A total of 383 patients met the criteria for clinical evaluability, and 174 were also bacteriologically evaluable; all treated patients were included in the safety analysis. Escherichia coli (86%) and Staphylococcus saprophyticus (4.6%) were the organisms most commonly isolated. Positive clinical responses were obtained 5 to 9 days after therapy in more than 92% of the patients in each group; sustained clinical cure rates 4 to 6 weeks after therapy were 78.3 and 76.9% in the sparfloxacin and ofloxacin groups, respectively. A positive bacteriologic response was observed in 98% of the bacteriologically evaluable patients in each treatment group at 5 to 9 days posttherapy and in 88.2 and 92.6% of the patients in the sparfloxacin and ofloxacin groups, respectively, 4 to 6 weeks after therapy. Almost 90% of all adverse events were of mild or moderate severity; the most frequent events at least possibly related to drug treatment were those common to the fluoroquinolones, namely, nausea, diarrhea, headache, insomnia, and photosensitivity. Photosensitivity was more frequent in the sparfloxacin group (6.9% versus 0.5% in the ofloxacin group); insomnia was more frequent in the ofloxacin group (3.7% versus 1.0% in the sparfloxacin group). These data suggest that a once-daily, 3-day regimen of sparfloxacin is effective and generally well tolerated in the treatment of acute uncomplicated urinary tract infections.