1. In all three renin sub-groups of essential hypertension, the state of sodium balance determines the degree of participation of the renin-angiotensin system in sustaining high blood pressure. 2. Even the low-renin type can become renin-dependent when sufficient sodium depletion has been achieved. 3. The main difference between patients of these sub-groups appears to be their variable capacity to become depleted of sodium under standard dietary regimens.

1. The anti-hypertensive effect of converting enzyme inhibition was evaluated in twenty-three hypertensive patients (seven renovascular, four essential, four malignant, one scleroderma, three chronic renal failure, four primary or idiopathic aldosteronism). 2. In sixteen patients a single injection (1–4 mg/kg) of the inhibitor produced an immediate anti-hypertensive effect, which lasted up to 16 h. In six patients the anti-hypertensive effect of the inhibitor was significantly improved after sodium depletion. 3. Plasma renin activities increased and plasma aldosterone concentrations decreased consistently except in idiopathic aldosteronism. 4. Converting enzyme inhibition provides a direct way of defining the degree of renin-dependency of the hypertension. Accordingly, it can be used diagnostically and for planning appropriate therapy. Therapeutically, it could be advantageous in hypertensive emergencies because of its safety, specificity and capacity to reduce aldosterone secretion.