Fibroblasts possess several distinct mechanisms that control cellular adhesion to extracellular matrix macromolecules. Monoclonal antibodies to a 140-kilodalton (kD) cell surface glycoprotein inhibited the adhesion of fibroblastic Chinese hamster ovary cells to fibronectin-coated substrata but did not inhibit adhesion to substrata coated with vitronectin, laminin, serum, or other adhesive macromolecules. Thus the 140-kD glycoprotein appears to be involved in the fibronectin-mediated adhesion mechanism but not in other adhesion processes.