Development of renal hypertension and of renin-induced hypertension was studied in intact and in adrenalectomized rats. Experimental renal hypertension developed similarly in intact rats and in adrenalectomized rats maintained on 0.9% saline. Subcutaneous administration of purified rat renin for 9-10 days induced hypertension in intact rats. Administration of the same amount of renin to adrenalectomized rats maintained on 0.9% saline, however, failed to induce hypertension. Renin-induced hypertension was restored in adrenalectomized rats by the administration of aldosterone, corticosterone, or dexamethasone. These corticosteroids by themselves had no effect on blood pressure of adrenalectomized rats. If larger amounts of renin were administered to adrenalectomized rats, hypertension developed to a similar degree as that observed in intact rats. It is concluded that for the development of both renal hypertension and renin-induced hypertension the adrenal cortex is not essential.