An axisymmetric single-path model (ASPM) for gas transport in the lower airways was developed and validated. A single airway path was represented by a series of straight tube segments interconnected by leaky transition regions that provide for flow loss at the airway bifurcations. The finite element method was used to solve the Navier-Stokes, continuity, and species convective-diffusion equations for the flow field and the species concentration distribution in the airways. The model was validated by comparing its predictions to various experimental measurements, i.e., dispersion coefficients for unsteady dispersion of an inhaled pulse of inert gas (benzene) along an airway path encompassing five generations in a scaled-up model of Weibel's symmetric airway geometry, and mass transfer coefficients for steady inspiratory-directed flow of a reactive gas (formaldehyde) in both a single bifurcation and an airway path incorporating three generations of a symmetrically-branched physical model of the airways. For the latter problem, ASPM predictions were also compared with the results of three-dimensional finite element computations in the branched airway geometry. The ASPM results for the dispersion and mass transfer coefficients compared quantitatively well with both the experimental measurements and three-dimensional simulations. This is an abstract of a paper presented at the 2006 AIChE National Meeting (San Francisco, CA 11/12-17/2006).