The k-epsilon model was used to describe of airflow structure in the sequence of the two first bifurcations of the human respiratory system. Local and temporary distributions of the linear air velocity were calculated for a cyclic breathing pattern corresponding to symmetrical hyperventilation with spontaneous deep breathing. For such a flow, deposition efficiency of particles with diameters of 0.01, 0.1, 1 and 10 mum was calculated using particle trajectories including random displacement of particles due to the Brownian motion. For each type of particles, the "hot spots" of deposition were identified. A specific temporary deposition pattern during breathing cycle was found. The enhancement of deposition was observed at the moment of transition between inspiratory and expiratory parts of the breathing curve. (C) 2002 Elsevier Science Ltd. All rights reserved.