[en] A compartmental model to describe mucociliary transport and particle clearance in the tracheobronchial trees was described. A method was proposed for determining the mucociliary transport rate as a function of the airway depth from the retention curve directly. Each airway generation was represented by an escalator. For Weibel's lung model there were 17 airway generations in the tracheobronchial tree. The subject performed a series of respiratory mechanical function tests prior to exposure to a monodisperse ferric-oxide aerosol tagged with technetium-99. The model was simple and appeared to describe the physical process well