The effects of insulin hypoglycaemia (0.15 IU/kg) on plasma adrenaline, noradrenaline, dopamine, glucagon and pancreatic polypeptide (PP) concentrations were investigated in 6 adrenalectomized subjects and 6 healthy controls. Both the rise in mean plasma insulin and the fall in mean blood glucose concentration were closely similar in the two groups. Mean plasma adrenaline concentration rose by about 3 nmol/l in the normal subjects, but remained unchanged in adrenalectomized subjects. Mean plasma noradrenaline concentration increased by about 2 nmol/l in both groups. Despite the large difference in adrenaline concentrations during hypoglycaemia, there was no significant difference between the responses of the endocrine pancreas of the normal and adrenalectomized subjects. Thus, mean plasma glucagon concentration rose by about 30 pmol/l and mean plasma PP concentration by about 150 pmol/l in each group. We conclude that the release of glucagon and PP during hypoglycaemia does not depend upon changes in plasma adrenaline concentration in man.