A randomized, double-blind, double-dummy, three-arm parallel design, multicentre study was conducted among adult patients with acute exacerbation of chronic bronchitis (AECB) in order to compare the efficacy and safety of two different doses of levofloxacin with cefuroxime axetil. A total of 832 patients were randomized to receive oral levofloxacin (250 mg od or 500 mg od) or oral cefuroxime axetil (250 mg bd) for 7-10 days. The primary efficacy analysis was based on the clinical response in patients with bacteriologically confirmed AECB, determined 5-14 days after the end of therapy (per-protocol population). Of 839 patients enrolled (at 71 centres in 14 countries), seven were not treated, giving an intention-to-treat (ITT) population of 832. In total, 281 patients received levofloxacin 250 mg, 280 received levofloxacin 500 mg and 271 received cefuroxime axetil. The cure rates in the ITT population were: levofloxacin 250 mg, 70% (196/281); levofloxacin 500 mg, 70% (195/280); cefuroxime axetil, 61% (166/271); those in the per-protocol population were: 78% (121/156), 79% (108/137) and 66% (88/134), respectively. Both doses of levofloxacin were at least as effective as cefuroxime axetil and were active against the main pathogens of clinical relevance (Haemophilus influenzae, Streptococcus pneumoniae and Moraxella catarrhalis). All three treatment regimens were equally well tolerated. In conclusion, the results show that levofloxacin (250 mg and 500 mg) od is effective and well tolerated in the treatment of AECB in adult patients.