A correlative study of clinical, electrophysiological, quantitative, histopathologic and ultrastructural changes seen in 13 instances of the index branch of the radial cutaneous nerve was undertaken in leprosy patients. Testing by graded nylon proved to be more reliable than any other conventional clinical tests. The quantitative studies revealed that small-sized fiber loss was encountered in the early stages of nerve involvement in leprosy followed by loss of large-sized fibers with or without increase in small-sized fibers. Segmental dymyelination of small-sized fibers was seen in early stages of degeneration in leprosy nerves irrespective of type of leprosy. Wallerian degeneration was encountered in advanced stages with total destruction of the nerves. At the ultrastructural level clinically normal nerves of leprosy patients (LN series) showed minimal but significant changes, such as thickening of the basement membrane of perineurial cells, as well as an increase in the amount of collagen between the perineurial layers. Marked increases in the amount of endoneurial collagen were noticed. Axons devoid of myelin, probably demyelinated fibers, were occasionally observed. Slight proliferation of the basement membrane of the endothelial cells was also observed. These changes were of a more advanced nature in the clinically involved cases of leprosy (L series). Two BL types of cases from the L series, showed presence of M. leprae in Schwann cell cytoplasm of myelinated and unmyelinated fibers, perineurial cells, in endothelial cells and macrophages. In cases having impaired sensory modalities (L series), thickening of the perineurium was due to increase in the number of layers of perineurial cells in addition to the increase in collagen. Probably one of the ways in which unmyelinated fibers degenerate is by splitting the Schwann cell columns and extrusion of the axons. Collagen pockets were seen in the LN series of cases. These are probably the degenerated nonmyelinated fibers being replaced by collagen fibrils. Postoperative clinical charting was done on the patient whose IRC nerves were removed. It showed complete restoration of all modalities of sensation in the area of its distribution by the end of three months.