Receptor autoradiography was used to determine the distribution of binding sites for monoaminergic and cholinergic neurotransmitters in the cat median eminence. Results showed that binding sites were differentially distributed in that [3H]-p-aminoclonidine (an alpha-2-adrenergic ligand) and [3H]pyrilamine (an H1-histaminergic ligand) binding were concentrated in the medial region of the external layer of the median eminence while [3H]lysergic acid diethylamide (a serotonergic ligand) and [3H] quinuclidinyl benzilate (a muscarinic cholinergic ligand) binding were concentrated within the lateral region of the external layer. These patterns are coincident with the differential distribution of hypophysiotropic hormones in the median eminence, suggesting that monoamines and acetylcholine may regulate the release of these hormones at the level of the median eminence.