Confronting subsurface cisternae (CSC) and desmosomes are abundant at sites of parallel apposition of plasma membranes in confluent epitheloid monolayers of HeLa cells. Both structures are absent in young and subconfluent cultures, where stable intercellular contacts do not occur. They first appear when the plane of intercellular contact approaches towards the vertical; they disappear when cells separate spontaneously at superconfluency or by treatment with EDTA. The structure of CSC, lacking ribosomes at their side facing the plasma membrane, might fit the production of glycoproteins involved in intercellular adhesion.