A freeze-fracture study of affected and unaffected psoriatic skin has demonstrated the presence of marked modification of the plasma membrane in the psoriatic lesion. In the lower layers of the epidermis, an increase of membrane associated particles was observed in many keratinocytes, possibly representing the morphological intramembranous equivalent of changes in the outer cell membrane demonstrated with cytochemical techniques. Furthermore, in the malphighian layer, numerous gap junctions have been found, which may be interpreted as a phenomenon compensating the uncontrolled proliferation, and may represent a point of differentiation between cell proliferation in psoriasis and neoplasia. This technique confirmed the poor tendency to adhesion of keratinocytes in extrajunctional areas, which had already been shown by other morphological techniques.