From November 1991 through March 1992, nasal and pharyngeal swab samples were collected from 45 bison (Bison bison) from Yellowstone National Park, Montana (USA) and cultured for Pasteurella spp. Thirteen isolates of Pasteurella spp. were recovered from 10 (22%) of the animals. Ten isolates were from pharyngeal samples in contrast to three isolates from nasal samples. Pasteurella haemolytica (six biotype T, two biotype A, and two biotype 3) was the predominant Pasteurella species. Five biotype T isolates were serotype 4 and the sixth agglutinated in antisera 3, 4, and 10. Both biotype A isolates were untypable with antisera to recognized type strains. Pasteurella multocida was isolated from the pharyngeal samples of one animal. Two isolates could not be identified to species.