Qualitative descriptions of the surfactant film behaviour and the concept of hydrodynamical clearance in the alveoli are presented, and the possibilities of modelling of dynamics of this system mathematically are discussed. Using the model formulated it is shown that under dynamic conditions physiochemical surface phenomena may lead to net flow of the liquid layer (together with the dust particles) out of the alveoli. The effects of some parameters (surfactant activity and its production, viscosity of the liquid layer, size and geometry of the bronchoalveolar system, shape of respiratory curve) on the clearance rate are demonstrated. The results obtained are discussed critically.