Three cDNA clones homologous to rat neuronal nicotinic receptors were identified in a human brain stem library by screening at low stringency with a mixture of rat alpha 5, beta 2 and beta 4 subunit probes. Positive clones were further analysed by hybridisation at higher stringency with individual rat nicotinic receptor probes. One positive clone was found to encode a protein that exhibited characteristic features of a member of the ligand-gated ion channel class of protein subunits, and showed 89% homology with a rat beta 3 neuronal nicotinic receptor subunit. Northern blots demonstrated the presence of a 1.7 kb transcript in RNA extracted from adult human Pons. This clone has therefore been designated the human beta 3 neuronal nicotinic receptor subunit.