The efficacy and safety of two oral dosing regimens of gatifloxacin were compared to ciprofloxacin in the treatment of complicated urinary tract infection in a randomised, double-blind multi-centre trial. One thousand one hundred and twenty-three adult patients with complicated urinary tract infection (70%) or pyelonephritis (30%) were initially enrolled, 1122 were treated. Of these, 824 were included in a modified ITT population: gatifloxacin 200 mg (274 patients) or 400 mg (280 patients) once daily or ciprofloxacin 500 mg twice daily for 5-14 days (269 patients). Bacteriological and clinical responses were assessed 7-9 days after the end of treatment (EOT) and 4-6 weeks post-treatment (end of study visit, EOS). The bacteriological response rates per patient at EOT in the gatifloxacin 400 mg, gatifloxacin 200 mg and ciprofloxacin groups were 77% (207/269), 78% (208/268) and 73% (190/259), respectively. At EOS they were slightly lower: 70% (184/262), 71% (176/248) and 69% (174/252), respectively. The clinical responses at EOT were 69% (190/277), 70% (190/273) and 65% (174/266). At EOS they were 71% (193/273), 70% (182/259) and 74% (190/258). The overall eradication rates of initial pathogens at EOT and EOS were 85.3% and 88.4% in the gatifloxacin 400 mg group; 84.1 and 90.1% in the gatifloxacin 200 mg group and 85.1 and 91.4% in the ciprofloxacin group. Both oral regimens of gatifloxacin were as effective as that of ciprofloxacin. All treatment groups showed a similar safety profile, nausea being the most frequently reported adverse event.