Partial cDNA clones generated by RT-PCR were used as probes to clone the cDNAs encoding the human alpha 4 and beta 2 neuronal nicotinic acetylcholine receptor (nAChR) subunits. The 2.1-kb alpha 4 cDNA shows 84 and 76% identity to the rat and chicken cDNA sequences, respectively. The deduced amino-acid sequence shares 89 and 84% similarity, respectively, with the corresponding rat and chicken proteins, with most of the divergence occurring in the cytoplasmic domain. The 1721-nucleotide beta 2 sequence was identical to the human beta 2 sequence previously reported. Transfection of the alpha 4 and beta 2 clones into HEK293 cells resulted in the formation of binding sites that display high affinity towards [3H] cytisine, a characteristic of the alpha 4 beta 2 subtype produced in vivo.