Aminergic regulation of growth hormone (GH) and prolactin (Prl) was studied in male adolescent baboons by i.v. infusion of dopamine (DA), norepinephrine (NE), thyrotropin-releasing hormone (TRH), phentolamine, haloperidol, and inhibitors of DA-β-hydroxylase and peripheral decarboxylase. 20-min infusion of DA (40 µg/kg·min) and 60-min infusion of NE (0.4 µg/kg·min) stimulated GH release. The DA-induced GH release was suppressed by concomitant infusion of FLA 63 (inhibitor of NE synthesis from DA) and by phentolamine, indicating α-adrenergic mediation of GH release. Micro-injection of DA (0.8 µg/kg) into the medial basal hypothalamus (MBH) lowered basal GH. Prl was released by i.v. TRH, and this effect was suppressed by i.v. DA but not by i.v. NE. Blockade of peripheral decarboxylase by carbidopa elicited a marked and sustained rise in Prl which was inhibited by i.v. DA. Microinjection of NE (0.8 µg/kg) into the MBH released Prl. These data indicate that in the MBH, α-adrenergic mechanisms release GH and Prl, and that dopaminergic mechanisms sup