The Tupaia belangeri yunalis (tree shrew) is one of the primitive primates. They were inoculated subcutaneously in the footpad or intravenously with Mycobacterium leprae from a patient with multibacillary leprosy. As controls, the footpads of CFW mice were inoculated with the same suspension of M. leprae. The results showed growth of acid-fast bacilli (AFB) in the footpads of locally inoculated CFW mice and in the footpads of both locally and intravenously inoculated tupaias. Whereas the numbers of AFB declined in the footpads of CFW mice after 12 months, they increased in the tupaia footpads, up to 2.44 x 19(9) AFB/g of tissue. The footpads of one tupaia were swollen, which on section revealed a granulomatous infiltration, including foamy and heavily infected macrophages. M. leprae were also seen in the branches of cutaneous nerves. Also AFB occurred in some viscera. Preliminary studies indicate that the AFB multiplying in tupaias are M. leprae.