OBJECTIVES: The efficacy and safety of levofloxacin and lomefloxacin in complicated urinary tract infections (UTIs) were compared in a randomized, open-label, multicenter study. METHODS: Outpatients were randomized to receive levofloxacin (250 mg once daily) for 7 to 10 days or lomefloxacin (400 mg once daily) for 14 days. Three hundred thirty-six patients (171 with levofloxacin, 165 with lomefloxacin) were evaluable for microbiologic efficacy, and 461 patients (232 with levofloxacin, 229 with lomefloxacin) for safety. RESULTS: The overall microbiologic eradication rate of pathogens was 95.5% (168 of 176) for levofloxacin and 91.7% (154 of 168) for lomefloxacin. Eradication rates with respect to patients were 95.3% (163 of 171) and 92.1% (152 of 165) for levofloxacin and lomefloxacin, respectively. At the 5 to 9-day post-therapy visit, symptoms were completely resolved in 84.8% of levofloxacin-treated patients and were decreased in 8.2% (93.0% clinical success). Among the lomefloxacin-treated patients, complete resolution was seen in 82.4%, with decreased symptoms in 6.1% (88.5% clinical success). Drug-related adverse events (AEs) were reported by 10 (2.6%) and 18 (5.2%) levofloxacin- and lomefloxacin-treated patients, respectively. Compared with levofloxacin-treated patients, more lomefloxacin-treated patients experienced photosensitivity reactions (3 [1.3%] versus 0) and dizziness (2 [0.9%] versus 0). Nausea (3 [1.3%] versus 1 [0.4%]) was more frequent in the levofloxacin-treated group. Six patients in each treatment group had a gastrointestinal AE (1.7%); rash was reported more frequently with lomefloxacin (4 patients [0.4%]) than with levofloxacin (1 patient [0.4%]). Discontinuation because of AEs was observed in 8 (3.4%) levofloxacin- and 14 (6.1%) lomefloxacin-treated patients. CONCLUSIONS: Once-daily levofloxacin is as effective as and has a superior tolerability profile than lomefloxacin in the treatment of complicated UTIs.