A model describing passive accumulation of organic chemicals from the aqueous environment and contaminated food in fish is developed. The model considers both biological attributes of the fish and physicochemical properties of the chemical that determines diffusive exchange across gill membranes and intestinal mucosa. Important biological characteristics addressed by the model are the fish's gill morphometry, feeding and growth rate, and fractional aqueous, lipid, and nonlipid organic composition. Relevant physicochemical properties are the chemical's molar volume and noctanol/water partition coefficient (Kow), which are used to estimate the chemical's aqueous diffusivity and partitioning to the fish's lipid and nonlipid organic fractions, respectively. The model is used to describe and to analyze the bioaccumulation of polychlorinated biphenyls (PCBs) in Lake Ontario alewife (Alosa pseudoharengus), coho salmon (Oncorhynchus kisutch), rainbow trout (Oncorhynchus mykiss), brown trout (Salmo trutta), and lake trout (Salvelinus namaycush).