Participation of the neuronal nicotinic receptor subunit alpha6 in a physiologically relevant receptor has yet to be demonstrated, but its high degree of expression in catecholaminergic nuclei has attracted considerable interest. To investigate the pattern of expression of the alpha6 protein, a subunit specific antibody against the alpha6 subunit was used to immunohistochemically label sections of the adult rat brain. Alpha6 immunoreactivity was found to be present in the substantia nigra, the ventral tegmental area, the locus coeruleus and the medial habenula, and double-labeling for tyrosine hydroxylase demonstrated that the alpha6 protein is present on dopaminergic neurons of the midbrain. A possible role for the alpha6 subunit in nicotinic modulation of dopaminergic transmission is therefore proposed.