AbstractThe amount of the neural retina cell recognition protein, R‐cognin, in the plasma membrane of chick embryo neural retina cells declined 43% between 10 and 17 days of embryonic development. Over this period there was a 27% increase in the plasma membrane content of the α‐bungarotoxin receptor. Plasma membranes of both these ages were sonicated into vesicles and these vesicles partitioned on α‐bungarotoxin agarose beads into those which contained detectable α‐bungarotoxin receptor and those which did not. At 10 days, approximately 6% of the plasma membrane vesicles contained receptor. At 17 days, <2% did. At 10 days, 60% of the R‐cognin was found in the α‐bungarotoxin receptor‐containing vesicles, at 17 days 86%. At 17 days, 6% of the retina membrane with a high concentration of both α‐bungarotoxin receptor and R‐cognin was of a density indicative of it being of synaptic origin. These results suggested that R‐cognin and α‐bungarotoxin receptor occurred close together in the plasma membrane of retina cells. However, the lack of competition between R‐cognin gamma globulin and specific α‐bungarotoxin binding indicated that the α‐bungarotoxin receptor and R‐cognin were not the same protein. Thus, R‐cognin and the α‐bungarotoxin receptor appear to be separate proteins which occur in close proximity on the retina plasma membrane.