Partial cDNA clones generated by RT-PCR were used as probes to clone the cDNAs encoding the human α4 and β2 neuronal nicotinic acetylcholine receptor (nAChR) subunits. The 2.1-kb α4 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 β sequence was identical to the human β2 sequence previously reported. Transfection of the α4 and β2 clones into HEK293 cells resulted in the formation of binding sites that display high affinity towards [³h]cytisine, a characteristic of the α4β2 subtype produced in vivo