Transport in the conducting region of the human airways affects many diagnostic and therapeutic procedures. In this work, convective mass transport is characterized by a transport profile that is used to (1) investigate the significance of simple streaming and augmented dispersion mechanisms, and (2) understand steady streaming in the human airways. Laser-induced fluorescence experiments and numerical simulations were performed to assess transport profiles on inspiration and expiration for a range of Reynolds numbers at various locations in a three-generation model of the conducting region of the lung. The shape of the transport profile was found to be largely independent of generation, branch, flow direction, and Reynolds number. Simple streaming was relatively more important to convective dispersion than augmented dispersion. An alternative explanation for steady streaming, based on geometric asymmetries associated with a bifurcation network, is presented. (C) 2008 Elsevier Ltd. All rights reserved.