A large family of glycoproteins mediates cell adhesion by binding to cellular receptors. As a group, these adhesive proteins are large in size, multi-domainal in composition, and are capable of self-association. A general property of the adhesive proteins is their susceptibility to structural modulation, and conformational change provides a mechanism for regulation of their adhesive functions. To illustrate this concept, conformational alterations of thrombospondin, fibrinogen and fibronectin are shown to modulate their adhesive potential. Thus, conformational status of the adhesive proteins contributes to the regulation of cell adhesion.