If the right postganglionic cardioaccelerator nerves of cats are stimulated (2 Hz), dopamine, in the presence of cocaine, inhibits transmission. This inhibitory response is prevented by low doses of haloperidol. Phentolamine produces some antagonism and phenoxy-benzamine produces no antagonism to the dopamine-induced inhibition. It is postulated that dopamine receptors on the adrenergic nerve terminals modulate norepinephrine release.