This article discusses the validity of describing single-breath, gas or aerosol bolus transport processes in terms of effective Gaussian characteristics. This is done in the context of a comparison between the predictions of a recent macrotransport model of pulmonary transport phenomena and predictions based upon the numerical solution of a so-called ＇exact＇ microtransport problem. In addition, comparison is made with the predictions of a former network model of convective dispersion in the conducting airways of the lung. For conditions of physiological interest, the macrotransport model is shown to predict to within reasonable accuracy the mode (i.e., time of exit of the peak of an inspired bolus) as well as the dispersion of gas or aerosol for the case of an impulsive introduction of the gas/aerosol bolus (varying the shape and size of the bolus). The relative merits of micro-and macroscopic descriptions of lung transport problems are discussed. Comparisons with experimental data, as well as a discussion of the implications of the present study on the future development of transport models of lung dispersion, are provided.