Abstract: The human neuroblastoma clone SH-SY5Y expresses potassium-, carbachol-, and calcium ionophore A23187-evoked, calcium-dependent release of [3H]noradrenaline. Release in response to carbachol and potassium was greater than additive. Atropine (Ki= 0.33 nM), hexahydrosiladifenidol (Ki= 18 nM), and pirenzepine (Ki= 1,183 nM) completely inhibited the carbachol-evoked noradrenaline release, an order of potency suggesting that an M3 receptor was linked to release. In contrast, noradrenaline release was only partially inhibited by the M2-selective antagonists meth-octramine (10-4M) and AFDX-116 (10-4M), by ∼14 and 46%, respectively. The nicotinic antagonist d-tubocurarine (10-4M) resulted in a partial inhibition of release, a finding suggesting that a nicotinic receptor may also be involved. SH-SY5Y provides a suitable cell line in which to study the biochemical mechanisms underlying the cholinergic receptor regulation of noradrenaline release.