Twenty-three patients with exacerbations of chronic bronchitis were divided in two groups in a randomized fashion receiving either amoxicillin 1500 mg/d (n = 13) or amoxicillin 1500 mg/d associated with the mucolytic drug ambroxol 90 mg/d (n = 10). The improvement in cough, expectoration difficulties and sputum purulence was statistically more evident and occurred earlier in the ambroxol + amoxicillin group than in the amoxicillin only group. Although amoxicillin plasma and sputum levels were similar in both groups, the differences in daily sputum volume, which was also statistically greater in patients receiving ambroxol, suggests that this drug favours the bronchial mucus clearance of the antibiotic which could be related to the more favourable clinical evolution. No changes were observed in lung function tests and blood gases.