Biopsies from normal and malignant human oral epithelium were studied electron histochemically using lanthanum nitrate for a selective demonstration of junctional complexes at the plasma membrane of adjacent cells. The heavy metal complex was found to settle irregularly, sometimes in intimate proximity to the epithelial cell, in areas corresponding to the glycocalyx, gap junctions, desmosomes and nonspecific contact areas. Tight junctions were rarely seen. The lack of these morphological adhesive areas, the desosomal detachment seen between cancer cells and the increased lanthanum-positive cell surface may be possible factors responsible for the dissociation of oral malignant cells.