SUMMARYIn order to evaluate the effect of alpha‐1 adrenoreceptor regulation of ACTH release during insulin‐induced hypoglycaemia, we studied the response to hypoglycaemia with and without prazosin premedication in eight normal men. Prazosin pretreatment did not affect basal or peak plasma ACTH, Cortisol or GH during hypoglycaemic stress. However basal plasma levels of noradrenaline were increased (P<0.02) as were responses of AVP, angiotensin II (P<0.05) and noradrenaline (P<0.05) to hypoglycaemia after prazosin. Though it is possible that these augmented responses masked an inhibitory effect of prazosin, we were unable to demonstrate a major role for alpha‐1 adrenergic receptors in mediating the ACTH response to hypoglycaemic stress in norma