Insulin stimulation was found to promote association of the alpha(v) beta(3) integrin (a vitronectin receptor) with insulin receptor substrate-1 (IRS-1), an intracellular protein that mediates insulin signaling by binding other signaling molecules, including growth factor receptor-bound protein 2 (Grb2) and phosphatidylinositol-3’ kinase. Insulin-treated cells expressing the alpha(v) beta(3) integrin showed 2.5 times more DNA synthesis when plated on vitronectin than on other substrates, whereas cells expressing another vitronectin receptor, alpha(v) beta(5), did not show this difference. The association between integrin and IRS-1 may be a mechanism for the synergistic action of growth factor and extracellular matrix receptors.