Studies on normal subjects have shown Summarythat blood-angiotensin-it levels are not markedly altered by postural change and sodium restriction, while more prominent increases are caused by acute administration of diuretics and oral contraceptive therapy. In benign and uncomplicated essential hypertension, blood-angiotensin-II levels are usually normal. However, increased levels are commonly present in patients with severe essential hypertension, renal hypertension, and malignant hypertension, with a significant correlation between diastolic pressure and blood-angiotensin-II concentration in all three forms of hypertension. The association with high blood-angiotensin-II is particularly frequent in malignant hypertension and renal hypertension, being observed in 90% of patients with these conditions. It is proposed that high levels of circulating angiotensin II may contribute to the development of renal hypertension in man, and that the ability of the diseased kidney to compensate for the pressor effects of high angiotensin levels by adjusting sodium and fluid balance may be an additional determining factor in the development of hypertension associated with renal disease.