Binding of concanavalin A (con A) to the lymphocyte surface at room temperature leads to restriction of the mobility of a variety of cell surface receptors including those from immunoglobulin (Ig), O, H-2, beta2-microglobulin, Fc receptors results in "co-capping" of Ig, H-2, theta, Fc receptors, as well as receptors for other lectins. Addition of colchicine to the cell suspensions reverses this effect and allows Con A receptors as well as other receptors to form patches and caps. Capping of Con A receptors, and beta2-microglobulin in the absence of ligands specific for these receptors. Receptors binding Limulus hemagglutinin and wax bean agglutinin, as well as those interacting with carbohydrate-specific antibodies, were partially co-capped with Con A but receptors for wheat germ agglutinin were not co-capped, excluding the possibility that restriction of receptor mobility by Con A resulted simply from cross-linkage of mobile receptors to immobilized glycoproteins (Con A receptors). Latex beads and platelets coupled to Con A were bound to lymphocytes under the same conditions as free Con A. Binding of these particles to local regions of the cell surface resulted in restriction of the mobility of those receptors that could be co-capped with free Con A. In contrast to the findings with free Con A, however, addition of colchicine resulted in capping of the bound particles but did not cause co-capping of either the unbound Con A receptors or other receptors. These findings support the hypothesis that modulation occurs via a submembranous assembly containing microtubules, and they further suggest that the transitions of this assembly induced locally by Con A may be propagated via cooperative processes.