OBJECTIVES: To evaluate, in two randomized, multicenter trials, levofloxacin compared with ciprofloxacin and lomefloxacin for efficacy and safety in treating acute pyelonephritis. METHODS: We enrolled a total of 186 patients with bacteriologically proved infection. Of these, 89 patients in both trials combined received levofloxacin 250 mg once daily; 58 received ciprofloxacin 500 mg twice daily in the first trial (double blind); and 39 received lomefloxacin 400 mg once daily in the second trial (open label). Microbiologic response of patients evaluable for microbiologic efficacy was the primary efficacy variable, and clinical response of microbiologically evaluable patients was the secondary efficacy variable in both studies. RESULTS: Escherichia coli was the most prevalent pathogen. At 5 to 9 days after the end of treatment, 95% of uropathogens were eradicated in patients who received levofloxacin compared with 94% in the ciprofloxacin-treated group and 95% in the lomefloxacin-treated group. The clinical cure rate was 92% for levofloxacin in both studies combined, 88% for ciprofloxacin, and 80% for lomefloxacin. Drug-related adverse events were reported by 2% of levofloxacin-treated patients, 8% of ciprofloxacin-treated patients, and 5% of lomefloxacin-treated patients. CONCLUSIONS: The once-daily oral administration, proven efficacy, and good tolerability make levofloxacin an excellent choice for empiric treatment of acute pyelonephritis.