The efficacy and safety of roxithromycin (300 mg once daily) and doxycycline (200 mg once daily) in the treatment of acute exacerbations of chronic bronchitis in general practice were compared in a multicenter, double-blind, double-dummy trial. The data presented here are the results of an interim analysis of 76 patients. A satisfactory clinical response was obtained in 81% of patients treated with roxithromycin and 80% of those treated with doxycycline. Among patients receiving roxithromycin, 12.2% volunteered adverse events, compared with 33% of those receiving doxycycline; the test treatments were considered possibly or probably responsible for the adverse events in 9.8% and 21.2% of cases, respectively. Though patient numbers are too small for statistically significant differences to be detected, we conclude that the results to date suggest that roxithromycin and doxycycline are equivalent in terms of efficacy, but that roxithromycin is better tolerated.