The differentiated function of epithelial tissues is dependent on the molecules which mediate the cohesion and polarization of the epithelium. Separate molecular families are responsible for the adhesion between adjacent cells and the adhesion between cells and the substratum. Using the kidney as a model of epithelial differentiation it has been shown that the assembly of a basal lamina containing the glycoprotein laminin and cadherin mediated intercellular adhesion are key events. The Wilms' tumour anti-oncogene plays a regulatory role in renal epithelial differentiation. Tissue modeling and tumour formation are both accompanied by reduced cell adhesion molecule function.