Cholesteatoma matrix, ear canal skin, postauricular skin, and middle ear mucosa were taken during middle ear surgery, and immunohistochemical technique was used to localize cytokeratin patterns of these tissues. In this study, we investigated differentiation of 4 different epitheliums using 5 monoclonal anti-epithelial keratin antibodies(AE) : AE-1, AE-2, AE-3, AE-5, AE-8. Several differences of cytokeratin patterns were observed between cholesteatoma matrix and postauricular skin as well as between cholesteatoma and middle ear mucosa. However, similarity of cytokeratin patterns was observed between cholesteatoma matrix and ear canal skin. These findings support the skin type epithelial origin of cholesteatoma matrix and strongly favor the immigration theory in the pathogenesis of cholesteatoma.