Cholesteatoma is characterized by the presence of a keratinizing epithelium in the middle ear. The accumulation of desquamous epithelial cells appears to be a crucial factor in the pathogenesis of the middle ear cholesteatoma. The accumulation of the keratin debris is due to the migration, proliferation, and differentitation of basal keratinocytes. In the present study, we investigated the expression of specific cytokeratins in the experimental cholesteatoma in gerbil to determine whether any difference of differentiation and proliferation between cholesteatoma and normal skin using several specific cytokeratin. Cytokeratin expression patterns of induced cholesteatoma and deep meatal skin were characterized by the presence of hyperproliferative cytokertin, but cholestestoma showed more intensely hyperproliferative charateristics and some atypical variations. These suggest that extensive accumulation of keratinous mass in external meatus may induce changes in cellualr diffrentiation and proliferation.