Moxifloxacin, a new respiratory quinolone, was compared with the macrolides azithromycin, clarithromycin and roxithromycin in a cohort study to assess clinical, safety and health-related outcomes of these antimicrobials in general practice settings. In total 332 patients with acute exacerbations of chronic bronchitis (AECB) each received one of the antimicrobial agents for a standard short course of therapy. Random allocation of therapeutic agents occurred by centre, not individuals, and the drugs were prescribed in an open manner. In addition to clinical evaluation by their physicians, all patients kept daily diaries to assess AECB symptoms over the study period, therapy received and quality of life. The overall clinical response rate was 96% and all four regimens were well tolerated. After 14 days there were no significant differences between the study groups, but analyses of patients' daily evaluations of certain AECB specific symptoms showed a faster response rate in the moxifloxacin group.