Desmosomes and keratinosomes serve a specific role in the complex process of keratinization and the formation of the horny layer. Their role is additional to the function of the tonofilaments and keratohyaline granules. Desmosomes serve as points of anchorage for the tonofilaments and give them orientation in the epidermal cells during their passage from the basal up to the horny layer. It appears likely that such orientation is necessary for normal keratinization to take place. Keratinosomes are associated with the rate of epidermal cell turnover and appear to be related to the transformation of granular cells into horny cells. Genetic acantholysis and dyskeratosis in Hailey-Hailey's and Darier's disease are due to either disruption or faulty synthesis of the tonofilament-desmosome complex. Genetic hyperkeratosis in epidermolytic ichthyosis is due to an increased turnover of epidermal cells. Genetic hyperkeratosis in dyskeratosis congenita of the mouth appears to be due to decreased shedding of cells from the horny layer.