The effect of surfactant on mucociliary transport has been studied in vitro on frog palate preparations. Surfactant obtained from pig lung was sprayed on frog palate and its effect on mucociliary transport, restored by the application of mucus, was compared with that of sprayed saline. Whereas saline induced a constant decrease in restored transport rate (mean +/- SEM = -37 +/- 3%, p less than 0.01), surfactant caused an increase in 5 of 6 experiments (+16 +/- 3%, p = NS). The difference between the 2 treatments was highly significant (p less than 0.001). Ambroxol has previously been shown to change the airway secretions of patients affected by chronic bronchitis; these secretions significantly improved mucociliary transport when applied to the frog palate. One may then speculate that the mucoactive effect of ambroxol in patients could be partly mediated by an antiadhesive effect of surfactant, production of which is increased by ambroxol, on cilia-mucus coupling on the surface of bronchial mucosa.