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This study reports niche relationships between elk (Cervus elaphus) and four other native ungulates, mule deer (Odocoileus hermionus), bison (Bison bison), pronghorn (Antilocapra americana), and bighorn sheep (Ovis canadensis), on the northern winter range of Yellowstone National Park during a period of release of elk from artificial controls. The investigation was conducted during winter from 1986 to 1988, a period of high ungulate density, and compared the data with similar observations gathered by Barmore (1980) for the winters of 1968-1970, a period of low ungulate density. Two ungulate species exhibited evidence of possible increased intra- or inter-specific competition following release from artificial controls, but three other species showed no such evidence. Neither elk, pronghorns, or mule deer exhibited any but the most minor changes in habitat use, habitat breadth, diets, or diet overlaps between period 1 and 2. The bison population increased by about 700%, and its occupied range increased by about 300% during the study periods; however, increased intra- and inter-specific competition was likely for bison. Bison increased their habitat breadth, while their habitat overlaps with all other ungulates increased from 25 to 39%, and their diet overlaps increased with two other grazing ungulate species. The bighorn sheep population was smaller during period 2, and its increased habitat and diet breadths more likely reflect increased interspecific competition due to large increases in those of the other grazers, elk and bison. Between periods 1 and 2, bighorn sheep increased their use of the sagebrush (Artemisia spp.) type, and they consumed more of the grasses commonly found in the sagebrush type. Bighorn sheep do not prefer tall shrubs, and their increased use of the sagebrush type during period 2 might reflect interspecific competition with elk.