Using the indirect immunofluorescence method, it has been shown for the first time that concanavalin A receptors can undergo a redistribution over the surface of platelets spread on the substrate. The distribution of receptors in the intact cells is diffuse and random. Con A receptors, cross-linked by their ligand, are removed from the surface of the lamellar cytoplasm of living substrate-spread platelets. These receptors move into the central part of cell surface. This phenomenon is similar to capping or clearing of lamellar cytoplasm of big nucleated cells. Cytochalasin B (10 mcg/ml) does not prevent the formation of patches of receptors but inhibits the clearing of the lamellar cytoplasm of spread platelets. This result suggests that microfilaments may be involved in the redistribution of receptors.