The efficacy and safety of a five-day course of cefuroxime axetil (250 mg b.d.) and a seven-day course of clarithromycin (250 mg b.d.) were compared in a large double-blind, randomised, multinational study involving 684 patients with acute exacerbations of chronic bronchitis. In an intent-to-treat analysis, the post-treatment clinical responses to each treatment were comparable (82%) and rates at follow-up were similar: 64% on cefuroxime axetil and 61% on clarithromycin. Pre-treatment pathogens were isolated from a total of 192 patients, Haemophilus influenzae being the most common. Overall pathogen eradication rates were similar for both treatments. Both treatments were well tolerated. In conclusion, a five-day course of cefuroxime axetil is clinically equivalent to a seven-day course of clarithromycin in the treatment of acute exacerbations of chronic bronchitis, and may have potential socioeconomic benefits.