We investigated the possible effects of the mucoactive drug Carbocysteine lysine salt monohydrate (CLS.H2O) on experimentally-induced airway inflammation and hyperresponsiveness. CLS.H2O given by the oral route (300 mg kg(-1)) significantly reduced neutrophil infiltration into the airway lumen induced by intratracheal injection of IL-1 beta in rats. In addition, CLS.H2O inhibited dose-dependently (100-300 mg kg(-1) p.o.) the formation of pleural exudate and leukocyte recruitment induced by intrapleural injection of carrageenan in rats. Because of the close interaction between the inflammatory process and the development of airway hyperresponsiveness we also tested CLS.H2O on cigarette-smoke-induced inflammation and hyperreactivity in anaesthetized guinea-pigs. The drug, given either by oral (300 mg kg(-1)) or aerosol route (30-100 mg ml(-1)), was able to reduce the increase in airway responsiveness induced by smoke and the associated cell recruitment detected in the bronchoalveolar lavage (BAL) fluids. These results suggest that CLS.H2O can exert an anti-inflammatory action in addition to its mucoregulatory activity. The anti-inflammatory and anti-hyperreactivity effect of the drug within the airways may be of advantage in the treatment of inflammatory lung diseases where mucus secretion together with airway inflammation and hyperreactivity contribute to airway obstruction.