It is well established that compounds that modify dopaminergic and cholinergic activity in man may induce changes in circulating growth hormone (GH). We have, therefore, investigated the effect of a dopamine agonist, bromocriptine, and a dopamine antagonist, domperidone, as well as a muscarinic cholinergic antagonist, pirenzepine, on the GH response to an analogue of GH-releasing hormone (GHRH) in normal male subjects. GHRH(1–29)NH2 induced a rise in serum GH that was augmented by bromocriptine, antagonized by pirenzepine, but was unaltered by domperidone. As this dose of GHRH(l-29) NH2 has been shown to be maximally stimulatory to GH release, it is suggested that there are dopamine stimulatory and cholinergic inhibitory receptors to GH release independent of GHRH in ma