Lanthanum has been used as a tracer for the intercellular space and the surface coats in different epithelia including human epidermis, however, lanthanum compounds may or may not penetrate into skin specimes and reaction product may or may not be present in the intercellular space. After treatment with alcian blue prior exposure to lanthanum the trilaminar plasma membrane was more regularly stained and a thin coat of reaction product corresponding to superficial glycoconjugates outlined the cell surface and filled the narrow intercellular space in normal epidermis. In psoriatic epidermis the quantity of superficial membrane-bound glycoconjugates was rather reduced, their distribution and compartmentalization was profoundly changed and the outer leaflet of the trilaminar plasma membrane was not always clearly seen, having a "moth-eaten appearance" in some places. These findings show once more that alterations of the cell membranes and their surface architecture are present in psoriasis. They may play a major role in the pathogenesis of the disease, influencing the activities of membrane-bound enzymes and the flow of the epidermal growth control mechanism. The glycocalyx may serve in this mechanism as an accumulator of energy rich compounds or as a receptor site of membrane-bound ezymes. According to our views it represents a "ground substance" of epidermal origin, which controls the social behaviour of the keratinocytes in tissue.