The Mongolian gerbil is a well-known animal model for induction of aural cholesteatomas. This animal model is useful for studying changes in the keratinizing epithelium. It is not known whether keratin accumulation can increase the proliferative activity of the keratinizing epithelium in tympanic membrane and meatal skin. In this study, we investigated the proliferative activity of the epidermis in induced aural cholesteatoma at various stages and in different areas of the tympanic membrane and meatal skin in normal gerbils. Anti-5-bromo-2- deoxyuridine (BrdU) was injected intraperitoneally to detect the proliferative activity of keratinizing epithelium. Immunohistochemistry with monoclonal BrdU antibody in the normal gerbil showed intense immunolabelled keratinocytes at the handle of malleus, and the superior parts of pars tensa and pars flaccida. Also, mitotic activity in the deep meatal skin was more active than in the lateral meatal skin. The induced aural cholesteatoma showed more active proliferation centre of the epithelial cell than eardrum and external ear canal of the normal gerbil. These observations suggest that the accumulation of the keratin debris might induce changes of the cellular proliferation in the external auditory meatus.