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The role of chemical constituents in the foraging behavior of black bears (Ursus americanus) was investigated using two field studies. Vascular tissue samples were collected from Douglas-fir (Pseudotsuga menziesii) trees recently foraged by black bears. Samples were extracted and analyzed by liquid and gas chromatography to determine carbohydrates and terpenes, respectively. Chemical data were subjected to correlation analyses and multiple regression to examine if they adequately describe observed foraging preferences. Free-ranging black bears also were offered a choice of four test diets that differed in content of carbohydrates and terpenes. Results indicated that forage preferences were based in part on chemical constituents in the forage. Black bears maximized intake of carbohydrates and minimized intake of terpenes. In multiple choice tests, free-ranging bears preferred a lowterpene diet to a high-terpene diet with identical carbohydrate content. Bears also preferred a high-carbohydrate diet to a low-carbohydrate diet with identical terpene content.