Studies were performed to determine whether antibodies prepared against nicotinic acetylcholine receptors (nAcChoR) from electric tissue are reactive toward nAcChoR-like antigenic determinants in rat brain. Reference experiments involved the use of Torpedo electroplax and rat innervated muscle as tissue controls and an anti-alpha-bungarotoxin antiserum as a probe for curaremimetic neurotoxin binding sites. As evinced by their ability to inhibit immunoprecipitation of Torpedo nAcChoR, brain or muscle membranes specifically interact with polyclonal antisera raised against Electrophorus electroplax nAcChoR. When the extent of polyclonal anti-nAcChoR antibody binding to muscle membranes is measured by protein A binding protocols, receptor-like antigenic determinants and toxin binding sites are found to be present in approximately equal quantities. In contrast, nAcChoR-like antigenic determinants on rat brain membranes are present at concentrations in excess of those of toxin binding sites. The results are consistent with the earlier observation that some antibodies prepared against nAcChoR from peripheral tissues recognize rat brain high-affinity alpha-bungarotoxin binding sites. The results also suggest the existence of nAcChoR-like entities in brain that do not bind toxin with a high affinity.