Psoriasis is a benign but hyperproliferative skin disease. Psoriatic basal cells show a phenotype similar to that of normal skin, while psoriatic suprabasal cells exhibit a qualitatively altered keratinization pathway, resulting in the absence of the granular layer. These cells further show an abnormal expression of cellular differentiation antigens, which does not lead to tumor development. This immunohistological study demonstrates the appearance of carcinoembryonic antigen (CEA) in psoriatic suprabasal cells below the parakeratotic layer, while other markers such as CEA-related antigens, the nonspecific cross-reacting antigens and alpha-fetoprotein are not expressed. CEA is absent in normal skin, lichen planus, ichthyosis vulgaris and allergic dermatitis. Our data support the notion that dedifferentiation of psoriatic suprabasal keratinocytes is due to the reactivation of early developmental patterns of differentiation in this disease.