Ligand-induced redistribution of concanavalin A (Con A) receptors on the surfaces of substrate-spread rabbit platelets was studied. These receptors were diffusely distributed on the surface of prefixed cells. Incubation of living cells with Con A and anti-Con A antiserum led to redistribution of corresponding receptors: These receptors were patched, removed from the upper surface of substrate-attached pseudopodia and lamellipodia, and accumulated on the surface of central cell parts. Capping of receptors was inhibited by cytochalasins B and D and by cold. Thus, capping of surface receptors can take place not only in large nucleated cells but also in platelets, that is, in small anucleate cell fragments. It is suggested that the cells of various types in the course of their attachment to the substratum form pseudopodia and lamellipodia that have a number of common characteristics, including the ability to move the cross-linked surface receptors centripetally.