Wind Cave National Park (WCNP) in southwestern South Dakota represents a vestige of the prairie ecosystem. American bison (Bison bison) are the most numerous ungulates in the Park and the largest herbivore. Thus bison have potential for considerable impact on the rangelands. Relatively few studies (Meagher 1973, Peden et al. 1974, Peden 1976, Reynolds 1978) were conducted on bison food habits. None was conducted on mid-grass prairies typical of WCNP. Dietary information is important for determining the value of the range to bison as well as management of bison in relation to other herbivores. The objectives of this study are to determine seasonal food habits of bison, key forage species, and how the bison interact with other major herbivores in range use.