Abstract. Non-culturable acid-fast bacteria from two spontaneous cases of so-called feline leprosy were transmitted to rats and cats and further passaged in rats or cats. Two to six months after infection, cats developed cutaneous lesions that were indistinguishable from spontaneous cases, including the occurrence of nasal granulomata in one cat. When injected into rats, the mycobacteria caused a generalized mycobacteriosis and the granulomatous reaction was composed chiefly of macrophages without polymorphonuclear granulocytes.Infection of cats with Mycobacterium Iepraemurium did not produce any lesions. The feline disease may be a suitable model for the study of human leprosy (Hansen's Disease).Cutaneous granuloma in domestic cats associated with acid-fast non-culturable bacteria have been described in New Zealand [2, 271, Britain [ 19, 281, Holland [2, 151, California [7], Oregon [24], and Canada [13, 201 and frequently are referred to as feline leprosy.Attempts to culture and identify the causative organisms in vitru all have failed, but transmission of the disease to laboratory animals has been successful in some instances. Mice and rats appear to be the most suitable species [l, 11, 15, 15, 191. The successful transmission of the disease to mice and rats gave rise to speculation that the causative agent might be Mycobacterium Iepraemurium [ 1 1, 151 and on the basis of comparative lepromin tests, the agent could be related to, if not identical with M . lepruemzrrium [ 121.The spectrum of cellular responses observed in spontaneous feline leprosy is quite similar to those described in leprosy in man [ 13, 20, 271. Since our initial report in 1974 [20], feline leprosy has been diagnosed in 44 cats at the Western College of Veterinary Medicine; 28 were classified as "tuberculoid" and 16 as "lepromatous" leprosy [ 131. All but one cat originated from the coastal regions of British Columbia. Attempts to culture the causative agents from nine cats on Lowenstein's, Stonebrinks, or other media at 37°C and at room temperature were 460