Abstract: Ultrastructural changes in peripheral nerve bio-psies from 5 cases.of tuberculoid leprosy, including 3 cases of active stage and 2 cases of regressive stage, were studied. Under electron microscopy, the nerve parenchyma from active stage was almost destroved and replaced by epithelioid cells, lymphocytes, macrophages and fibroblasts. Still some unmyel-inated and demyeliaated nerve fibers with intact or degenerated axon were seen amoag these cells. Occ-asionally polpmorphonuclear leucocytes, more or less collagen fibrils along with the changes in capillary walls were also found. Both intact and degenerated M. Ieprae could be seen in the cytoplasm of macrophages only after careful search, The predominapt feature of nerves from regressive stage was degenerated epithelioid cells, increasing number of lymphocytes and abundant formation of collagen fibrils. The pathogenesis of the lesions, the invasion route of M, leprae to the peripheral nerve were also discussed. The significance of the appearence of the polpmorphoriuclear leucocytes and collagen fibrils in the lesions of active stage was also elucidated.