Patients with chronic bronchitis were treated orally with either amoxicillin (500 mg) alone or in combination with carbocysteine (150 mg), thrice daily for five days, in order to assess whether the combination allows higher antibiotic levels to be obtained in bronchial mucus than those obtained from amoxicillin alone. Serum and mucus levels were determined for each patient at first and fifth day of the two drug regimens. The levels of amoxicillin in the lung tissue collected in patients undergoing pulmonary surgery were also determined after a single oral dose of amoxicillin (1 g) or of amoxicillin (1 g) plus carbocysteine (300 mg). In the bronchial secretions, at the same plasma concentrations, amoxicillin levels were statistically higher after administration of combined substances. These findings indicate the presence of a pharmacokinetic synergism between these compounds, which allows amoxicillin to penetrate more easily through the hemato-bronchial barrier. The association of amoxicillin and carbocysteine, determining an increase of the quantitative levels of antibiotic in the bronchial secretion (also if it is purulent), performs a sterilizing action in a short time with significant therapeutic advantages.