Recent topics of biochemical and biological progress in keratinization and dyskeratosis were reviewed and discussed. The main topics were as follows: (1) what is keratin (2) Differentiation of keratinocytes (keratinization), (3) Components of horny substances and their derivation, (4) Keratin filament and keratohyaline granule, (5) Synthesis of horny cell membrane (disulfide bonds, e- (T-glutamyl) lysine bonds), (6) Biochernical analysis of dyskeratosis (harlequin fetus, ichthyosis vulgaris, X-linked ichthyosis, lamellar ichthyosis, bullous congenital ichthyosiform erythroderma, psoriasis vulgaris, Dariers disease, M:enke's syndrome, Netherton's disease, Richner-Hanhart syndrome). These findings should lead to a more cornplete understanding of the pathologic events that occur in the process of keratinization and more rational therapy for many disorders in keratinization.