Several skin diseases and tumors were immunohistochemically studied with the use of monoclonal antibodies against myelin proteins and neurofilament proteins. In prurigo nodularis, many nerve fibers were found embedded in dense inflammatory cell infiltration. Abnormal innervation was observed in piloleiomyoma. The axons were demonstrated within the cytoplasm of granular cells of granular cell schwannoma. In neurofibroma, tumor cells had myelin proteins in their cytoplasms. Many cells and fibers that contained myelin proteins were demonstrated in nevus cell nevus, especially in compound nevus and intradermal nevus, and it was suggested that schwannian cells may be the origin of some nevus cells.