We have investigated the molecular basis of the organization of cell-substratum contact in normal and neoplastic renal epithelium. The several components of focal contacts and non-collagenous basement membrane glycoproteins have been identified by antibodies, detected by immunofluorescence and viewed by laser scanning microscopy. Tubular epithelial cells grown on glass coverslips expressed laminin at the cell periphery. Co-localized with laminin were receptors of the beta 1 integrin class, and the cytoplasmic plaque proteins vinculin and talin. When basement membrane glycoproteins laminin or fibronectin were exogenously supplied by growing cells on coated coverslips, the vinculin-, talin- and integrin-containing contacts became organized into linear arrays with intervening free cell membranes. Under these conditions the actin cytoskeleton became highly organized. By contrast some tumour cells showed a reduction in focal contact molecules and a failure to organize these structures in response to laminin or fibronectin. This loss of cell matrix interaction may be important during the progression of renal tumours.