Immunohistochemical methods play a very prominent role in the histological diagnosis of skin diseases. Their field of practical application, which initially was limited to patients with signs of autoimmunization, now includes several other nosological entities in dermatological histopathology, and particularly tumours. By using monoclonal or polyclonal antibodies, it is now possible to establish the diagnosis of poorly differentiated tumoral proliferations, such as carcinomas, melanomas, sarcomas, lymphomas, etc., to classify lymphomas according to their differential membrane antigens, or even to determine the histogenetic origin of tumours of unknown nature.