At present the detailed mechanism for transmembrane interactions is not known and a protein linked to the endoskeleton as well as to the exoskeleton has not been described as yet. The H2 complex, a transmembrane protein, consists of heavy and light chains, the latter is named beta-2-microglobulin. In order to look for an association of beta-2-microglobulin with an exoskeleton protein, we examined the extracellular matrix proteins, collagen type I, type IV, fibronectin, amyloid P, the solubilized glomerular basement membrane and lamiriin in respect to their interaction with the light chain. The heavy chain is known to bind strongly to the endoskeleton protein actin. Only laminin and the glomerular basement membrane bound firmly to the beta-2-microglobulin; 3 M urea was necessary to dissociate the formed complex. Incubation with beta-2-microglobulin antibody prevented binding of beta-2-microglobulin to laminin and the glomerular basement membrane on affinity chromatography columns. Antiserum to the glomerular basement membrane in turn prevented binding of beta-2-microglobulin to the glomerular basement membrane, whereas antibodies against the basement membrane collagen type IV failed to inhibit this binding to the glomerular basement membrane. Beta-2-microglobulin also bound to ñbronectin but this complex was dissociated with 1 M urea. In a rosette assay beta-2-microglobulin antibody and antiserum to the glomerular basement membrane reduced attachment of glomerular cells to beads coupled with laminin and solubilized glomerular cells to beads coupled with laminin and solubilized glomerular basement membrane. Also antibody against fibronectin reduced attachment of glomerular cells to fibronectin-coated beads. In an organ reconstruction assay, glomerular cells showed reduced binding to the glomerular scaffold if antibodies to the solubilized glomerular basement membrane or fibronectin were applied, but not if anti-type-IV collagen antibodies were used. This points to the role of laminin and fibronectin for the attachment to glomerular cells, where the receptor could be identified as beta-2-microglobulin, the light chain of the H2 complex, thus linking the endoskeleton with the exoskeleton. Only differences in the binding affinities between laminin and fibronectin were detected