We compared morphologic features of keratohyalin granules (KHG) that were directly related to keratinization in oral mucosa (tongue, cheek, gums, palate; n = 4) with those in parakeratotic epidermis (psoriasis, n = 2; pityriasis rubra pilaris, n = 1; acute dermatitis, n = 1) and normal orthokeratotic epidermis. Among others, the ultrastructural features of globular KHG were observed in the cheek, nonspecialized tongue mucosa, and parakeratotic epidermis occurring in psoriasis, pityriasis rubra pilaris, and acute dermatitis, whereas gums and palate showed a mixture of characteristics, also resembling stellate KHG as seen in normal skin. From literature as well as from our studies, the impression was gained that globular KHG were found especially in quickly dividing epithelia and could easily be distinguished from the irregular or stellate KHG that were found in slowly dividing normal epidermis. Therefore, we studied keratinization features on days 3, 7, and 14 after autografting normal human skin (n = 4), thus inducing high cell turnover. Stellate KHG, present in granular cells of normal skin, were almost absent on the third day. Active cell division on the seventh day resulted in sparse keratohyalin formation inside globular granules of low electron density, whereas numerous, rather electron-translucent lipid droplets occurred in upper spinous and horny cells. These two phenomena seemed to be interrelated. After 14 days, round and increasingly electron-dense KHG were noted.(ABSTRACT TRUNCATED AT 250 WORDS)