A model for the bioaccumulation of nonpolar, nonmetabolized organic chemicals by fish is described. The model, FGETS, simulates thermodynamically driven chemical exchange by fish assuming either aqueous exposure only or joint aqueous and food chain exposure. Parameterization of the model incorporates allometric relationships between the fish's body weight and its gill and intestinal surface areas, lipid content of the fish, and physico-chemical properties of the chemical (i.e., molecular weight, melting point, and n-octanol/water partition coefficient). The model is validated by comparing predicted and observed depuration rates of organic chemicals by rainbow trout (Salmo gairdneri). An application of the model describing the bioaccumulation of polychlorinated biphenyls by Lake Michigan lake trout (Salvelinus namaycush) also is presented.