Considering realistic tracheobronchial airways, transient airflow structures and micro-particle deposition patterns were simulated with an in-house finite-volume code for typical inhalation waveforms and Stokes numbers, i.e., the average flow rates at the trachea inlet, Q(in),(av), are 15 and 60 L/min and the mean Stokes number at the trachea inlet, St(mean,trachea), is in the range of 0.0229 <= St(mean,trachea) <= 0.0915, respectively. While the overall airflow fields exhibit similar characteristics, the local flow patterns which influence particle deposition are largely affected by secondary flows (for both Q(in,av) = 15 and 60 L/min) as well as airflow turbulence (when Q(in,av) = 60 L/min). The particle deposition fraction is a strongly transient function according to a given inhalation waveform. In light of the importance of targeted drug-aerosol delivery, it is shown that the relation between particle-release positions at the trachea inlet and particle depositions at specific lung sites are greatly influenced by the complex airway geometry and the flow-rate magnitude. For laminar flow, the particle-release points are deterministic and unique, as required for optimal drug-aerosol targeting. (c) 2007 Elsevier Ltd. All rights reserved.