Dietary comparisons based on fecal analysis of mule deer, elk, bighorn sheep, and cattle using mule deer winter ranges along the east slope of the Rocky Mountains indicated that elk, bighorn, and cattle diets were much more similar to each other than to mule deer diets. The greatest overlap between elk, bighorns, and mule deer occurred during late winter when creeping juniper became an important dietary item for all 3 species. Rank-order comparisons indicate that rankings of items in the graminoid and forb forage classes for diets of the 4 ungulate species were significantly correlated with availability of these items. Correlations between availability and diet rank-order were poor for items in the woody forage class. Differences in the diets of the 4 ungulate species were more pronounced at the forage class level than at the plant species/genus level. Resource management along the East Front of the Rocky Mountains in northcentral Montana is becoming one of the most important land use issues in the state. The lo-km-wide strip where the prairie and mountains meet encompasses winter ranges for wild ungulates summering in the Bob Marshall Wilderness, supports a viable cattle industry, and has recently become the center of intense oil and gas exploration activity. Development of oil and gas reserves in the area could alter the existing relationship between livestock and game species by converting rangeland to well sites, roads, or storage facilities and by increasing disturbance and harvest of native ungulates. To contend with these changes in land use, range mangers will require more precise knowledge of the manner in which native and domestic ungulates use available forage than was necessary in the past. This study compares diets of mule deer (Odocoileus hemionus), elk (Cervus elaphus) bighorn sheep (Ovis canadensis), and cattle from sites where concentrations of native ungulates winter. A partial assessment of dietary selectivity is included. Study Area The study area, located approximately 110 km northwest of Great Falls, Mont. (Fig. l), was characterized by shortgrass prairie intergrading with a narrow foothill region of fescue (Festuca sp.)wheatgrass (Agropyron sp.) grassland and limber pine (Pinusflexilis)woodland/savannah. Mule deer, elk, and bighorn sheep winter along the foothill zone from December through May. Most cattle grazing in the foothills occurs from May through October on private, U.S. Forest Service, and Bureau of Land Management holdings.