1. The pituitary-adrenocortical, sympathoadrenomedullary and renin-angiotensin-aldosterone systems contribute to circulatory and metabolic homeostasis during stress. One possible site of co-ordination of these systems is the beta-adrenoceptor. 2. To determine whether circulating beta-adrenoceptor agonists can act hormonally to stimulate these systems simultaneously, plasma concentrations of corticotrophin (ACTH), noradrenaline, adrenaline and plasma renin activity were measured during graded intravenous infusions of isoprenaline in 20 people. 3. Administration of isoprenaline caused dose-related increases in noradrenaline (94% at the highest dose) and renin activity (189%), but decreases in ACTH (25%) and adrenaline (20%), findings inconsistent with simultaneous activation of these systems by circulating beta-adrenoceptor agonists.