Immunohistochemical methods were used to study the possible co-localization of two α-bungarotoxin-sensitive (α7 and α8) and two α-bungarotoxin-insensitive (β2 and α3) subunits of the nicotinic acetylcholine receptors in neurons of the chick brain and retina. Several structures contained neurons that were doubly-labeled with antibodies against the α7 subunit and the β2 subunit. These structures included, for example, the interpeduncular nucleus, nucleus spiriformis lateralis, optic tectum, pretectal visual nuclei, and the lateral hypothalamus. Double-labeling with antibodies against the α7 and α8 subunits was also seen in several regions, which included the interpeduncular nucleus, visual pretectum, lateral hypothalamus, dorsal thalamus, and the habenular complex. In the retina, many cells in the inner nuclear layer were observed to contain α8 and α3 subunits, whereas neurons in the ganglion cell layer were seen to contain α7 and α8 or, less frequently, α7 and α3 subunits. These results indicate that α-bungarotoxin-sensitive and α-bungarotoxin-insensitive subunits of the nicotinic receptors are co-expressed by neurons of the chick brain and retina. © 1992.