ciated with the presence of tularemia in native animals. Pasteurella tularensis was cultured from ectoparasites (ticks, fleas, lice) of the black-tailed jackrabbit, Lepus calif or nicus, the antelope ground squirrel, Citellus leucurus, and the whitefooted deer mouse, Peromyscus maniculatus (Woodbury and Parker, 1953). The relationship between tularemia and the epizootics was not clearly revealed nor has it been fully clarified in the literature (Foshay, 1950). How the pathogen is maintained in the native fauna, how it is transmitted from animal to animal, and how it reappears from time to time are questions at best only partly understood. Records of animals naturally infected with tularemia are given by Burroughs et al (1945). Since the relative susceptibility of the various animals listed is not known, the present study of experimental infection was undertaken, using native animals of the Utah West Desert