A critical account of the development of immunohistochemical techniques and their adoption in histopathological diagnosis is given. The main topics presented are prostatic carcinoma (organ-specific markers), testicular tumors (histogenesis), urothelial carcinoma (differentiation antigens and early neoplastic lesions), and renal carcinoma (intermediate filaments). There is particular emphasis on the relations with histopathological problems and on new developments which it is thought will surpass histopathology in diagnostic capacity.