Two series of experiments were performed in nine healthy subjects. In series I, 96 single breath tests were performed in two subjects. The inspired gas contained 90% O2, 5% He and 5% SF6 and the slope of the alveolar plateau for N2, He and SF6 was computed. The following experimental conditions were considered variable: inspired volume with preinspiratory lung volume equal to residual volume or functional residual capacity (FRC), both with and without 10 sec breath-holding. In series II, each of the other 7 subjects performed 12 single breath N2 tests in which the subject inspired both 1 L and an inspiratory capacity (IC) of O2 from FRC with without 10 sec breath-holding. The main experimental observation is that without breath-holding the absolute value of the slope of the alveolar plateau is larger for 1 L inspiration than for an IC inspiration, whereas this volume dependence was smaller after 10 sec of breath-holding. Based on Milic-Emili model of the lung and on simulations of a multibranch point model of the acinus we concluded that, in so far as these models adequately describe gas distribution in the lung, intraregional parallel units presenting a sequential convective flow play an important role in the genesis of the alveolar plateau.