This prospectively randomized study compared fleroxacin, 400 mg once daily, with ofloxacin, 200 mg twice daily, administered orally for 7-14 days for the treatment of complicated urinary tract infection (UTI) in hospitalized, urologic patients. A total of 80 patients were enrolled in the study. Of these, 30 patients treated with fleroxacin and 35 treated with ofloxacin could be evaluated for therapeutic efficacy. Of the causative organisms, 29 of 30 in the fleroxacin group and 33 of 35 in the ofloxacin group were eliminated. One relapse occurred in the fleroxacin group and two in the ofloxacin group. Reinfection with gram-positive isolates was seen in five patients treated with fleroxacin and in one treated with ofloxacin. Thus, the cure rate was 24 (80%) of 30 in the fleroxacin group and 32 (91%) of 35 in the ofloxacin group. In general, both antibiotics were well tolerated. Four patients in the fleroxacin group and five in the ofloxacin group claimed mild, possibly drug-related adverse effects. The treatment of one patient in the ofloxacin group had to be discontinued because of an adverse effect (headache). Both fleroxacin and ofloxacin are effective and well-tolerated antibiotics for the treatment of complicated UTI.