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This paper describes the structure of the dynamic food-chain model PATHWAY and its utility for estimating radionuclide ingestion after fallout deposition from nuclear testing in Nevada. Model input requirements are described and output examples are provided. The basic output of PATHWAY is the time-integrated radionuclide ingestion by humans per unit fallout deposition (Bq per Bq m-2). Output specific to sex, age, life-style (diet), location (agricultural practice), event (calendar date), and radionuclide may be generated. Uncertainties of model predictions, based on "Monte Carlo" simulations using parameter value distributions, are described. Results of a sensitivity analysis, based on a ranking of partial correlation coefficients, are reviewed to illustrate the relative importance of parameters and associated transport pathways. Output data for 131I and 137Cs in milk are compared with predictions from several well known food-chain models. Preliminary efforts to validate PATHWAY results with real data sets are described.