Lomefloxacin is a new difluorinated quinolone antimicrobial agent with broad antibacterial activity and a long half-life which allows once-daily dosing. A multicenter, randomized trial was conducted to compare the safety and efficacy of once-daily oral lomefloxacin with twice-daily oral ciprofloxacin in the treatment of complicated urinary tract infections (UTIs). All 203 patients enrolled in the study had significant bacteriuria of - 10(5) colony-forming units/ml (CFU/ml) and clinical signs and symptoms of UTI such as dysuria, frequency, urgency, pain, or hematuria. Patients were randomized to receive either 400 mg lomefloxacin once daily (n = 101) or 250 mg ciprofloxacin twice daily (n = 102). The predominant baseline pathogen isolated from the patients in both groups was Escherichia coli. At the third visit (5-9 days post-treatment), 97.8% of patients in the lomefloxacin group and 96.8% in the ciprofloxacin group showed satisfactory bacteriologic results. Clinical success was achieved in 98.9% of patients in both treatment groups and there were no statistically significant differences between the two groups. Both drug regimens were well tolerated and no patient discontinued treatment due to adverse events. It was concluded that once-daily lemofloxacin was as effective as twice-daily ciprofloxacin in patients with complicated UTIs.