Egg lecithin may arrest blastogenic response of human peripheral blood lymphocytes mediated by different mitogenic lectins. Previous studies suggested that the inhibition may occur after lectin binding but before the cells are committed to the response. This was confirmed when it was presently shown that the lipid does not affect 125l-concanavalin A binding to lymphocytes nor does the lipid interact significantly with the lectin. The presence of the lipid however inhibits concanavalin A receptor capping and this occurred at similar concentration of the lipid as that required to arrest mitogenic response.