The deposition of inhaled particles within human nasal passages has important toxicologic and pharmacologic applications. However, experimental data quantitating factors affecting particle deposition are rare. The authors have evaluated findings from investigations employing either replica nasopharyngeal (NP) casts or surrogate model airways and compared them to each other and to human subject results. For ultrafine particles, studies using casts and models are incompatible, measured deposition values from the latter being lower by an entire order of magnitude. Possible sources of discrepancies between the data are suggested herein. Studies with diverse NP replicates, however, have yielded consistent deposition data over a wide particle size range, about 0.005 - 7 micrometers. Cast experiments underestimate, but in a systematic manner, in vivo information over a 0.5 - 3 micrometers interval. It is recommended, therefore, that NP replica cast data, rather than NP model airway data, be used to simulate human passages. For extrapolation modeling purposes, an original empirical formula based upon a logistic theory is derived which describes deposition over a particle size range of three orders of magnitude. (Copyright (c) 1992 Pergamon Press Ltd.)