A 6-month-old male rhesus monkey (Macaca mulatta) was inoculated intravenously and intracutaneously with Mycobacterium leprae obtained from a naturally infected mangabey monkey. The animal developed generalized lepromatous leprosy, and was killed for pathological examination 56 months after inoculation. Lesions were observed in the skin, nasal mucosa, peripheral nerves, and peripheral lymph nodes, with relative sparing of viscera. The monkey was carefully evaluated for the retrovirus STLV-III infection and was found negative. The rhesus monkey thus provides another animal model for the study of leprosy.