The deposition of aerosols in the lung is a complex process which involves a combination of several physical mechanisms, principally impaction, sedimentation and diffusion. The amount and distribution of deposition depends on the size and density of the particles and on the total inhalation rate. The overall pattern is determined by the levels of deposition at individual airway bifurcations, which in turn depend sensitively on the local branching geometry and air-flow held. Although the dependence on geometry is complex, it is well known that the effects of aerosol properties and inhalation rate on the local deposition mechanisms can be described primarily by just four dimensionless parameters: the Reynolds number (governing air flow), the Stokes number (governing impaction), a sedimentation (or gravitational) parameter and a diffusion parameter. In this paper we employ a diameter-based analysis of published morphometric data to examine how these four parameters vary with airway diameter under a range of conditions. Comparison between data for the human, the dog, the rat and the hamster shows reasonable agreement for the Reynolds and Stokes numbers, but differences between the human and the other species for the parameters governing sedimentation and diffusion. The predictions of Weibel＇s commonly used symmetrical model differ greatly from our estimates for all four parameters in the human.