1. Hypertension was produced in rabbits by unilateral renal encapsulation combined with contralateral nephrectomy or by the administration of calciferol and calcium lactate.
2. Weighed post mortem, the adrenal glands from the two hypertensive groups were significantly heavier than those from normotensive animals of similar weight. There was a direct correlation between the adrenal gland weight and the mean arterial blood pressure measured at the time of the terminal experiment.
3. The catecholamine content of the adrenal glands from the two groups of hypertensive animals was similar to that of the normotensive animals.
4. There was histological evidence of adrenal cortical hypertrophy in the glands of the hypertensive groups of animals.