Much controversy exists concerning the role of catecholamines in the control of ACTH secretion. In this study, noradrenaline (0.1 nmol-0.1 μmol/l) stimulated the release of both immunoreactive corticotrophin-releasing factor-41 (ir-CRF-41) and ir-arginine vasopressin (ir-AVP) from the rat hypothalamus in vitro. The stimulatory effect of noradrenaline on CRF-41 release was blocked by propranolol, whilst that on AVP release was blocked by phentolamine. γ-Aminobutyric acid (GABA; 10 nmol/l) inhibited the acetylcholine-induced release of both AVP and CRF-41 in vitro, and the effect was blocked by picrotoxin (0.1 μmol/l). Neither substance had any effect on the basal secretion of either neuropeptide. The results indicate that noradrenalin stimulates and GABA inhibits the release of both peptides from the rat hypothalamus in vitro.