1. Analysis of relationships between blood volume, vascular capacitance, cardiopulmonary and peripheral blood volumes, labelled albumin disappearance rate, plasma renin activity, blood pressure and age was performed in essential hypertensive males.
2. The results indicate that capacitance bed constriction probably occurs with age in essential hypertension leading to an increase in the product blood volume × vascular capacitance tone even in the presence of low blood volume.
3. A metabolic defect in the venous vascular bed along with an abnormality of regulation of renal sodium excretion is postulated.