The mucokinetic activity of ambroxol was demonstrated as an increase in mucus or particle transport rate on the frog palate and in guinea pig tracheas. To clarify the mechanism we examined the influence of the drug on the ciliary beat frequency (CBF) of isolated cells from guinea pig tracheas. Ambroxol significantly stimulated the CBF up to 10.8%, salbutamol up to 19.5%. The effect of ambroxol on CBF certainly contributes to, but does not explain the more pronounced increase in transport rate. Thus a stimulation of the mucociliary transport rate by the other major pharmacodynamic mechanisms, secretagogue activity and stimulation of pulmonary surfactant, has to be considered. The therapeutic activity of ambroxol in models of the infant and adult respiratory distress syndrome and of the chronic bronchitic syndrome is reviewed.