The expression and function of integrin subunits was examined by immunohistochemical staining of normal and malignant tissues and by producing specific changes in avian beta subunit cDNA that were subsequently expressed in mammalian cells. Most tissues express only a restricted number of integrins. These include primarily those thought to function as collagen/laminin receptors. With the exception of metastatic melanomas, tumors show a general down regulation of integrins. Structure/function studies of the beta subunit show that the cytoplasmic domain is required for inclusion in adhesion plaques and for promotion of adhesive functions; that the transmembrane domain is required for subunit association, but not proper alpha subunit selection; and that the amino terminal one third of the subunit must remain intact for subunit selection and ligand binding to occur.