In a retrospective study, the clinical and microbiological efficacy of amoxycillin-clavulanic acid and ciprofloxacin were evaluated in outpatients observed within the previous year who were affected by acute purulent exacerbations of chronic bronchitis. Of the 95 patients included in the trial, 50 received amoxycillin 875 mg-clavulanic acid 125 mg 8-hourly for 10 days and 45 received ciprofloxacin 500 mg 12-hourly before meals for 10 days. Of the amoxycillin-clavulanic acid-treated patients, 90% showed clear clinical improvement and in 10% treatment failed. In the ciprofloxacin group, 75.5% of patients showed improvement and in 24.5% treatment failed. All pathogens isolated prior to therapy were susceptible to the antibiotic used for therapy. At the end of treatment, in the amoxycillin-clavulanic acid-treated group, 84% of strains were eradicated and 8% persisted; others were superinfections. In the ciprofloxacin group, 57.7% of strains were eradicated, 26.6% persisted and 15.5% were superinfections. No clinically significant side effects were observed in either group. Overall, amoxycillin-clavulanic acid demonstrated superior clinical and microbiological efficacy to ciprofloxacin, although this might be attributable to the higher proportion of aerobic Gram-negative pathogens in the ciprofloxacin group.