SUMMARYPlasma aldosterone (PA), plasma renin activity (PRA), extracellular fluid volume (EFV) and hepatic blood flow were measured in forty‐four patients with sustained essential hypertension and compared with forty‐two normotensive controls of same age and sex. All patients had inulin clearances within the normal range and balanced sodium intake and urinary output. In hypertensives, PA, PRA, EFV and hepatic blood flow were within normal ranges; the log‐ratio PA: PRA was significantly elevated (P<0·001). In normotensives, a negative relationship was observed between PA and EFV (r= ‐0·55;P<0·001) while a positive relationship was observed between PA and PRA (=+0·70;P<0·001). In hypertensives, the two relationships were disrupted or less significant: for a given value of EFV, PA was more elevated in hypertensives than in normotensives; for a given value of PRA, PA was more elevated in hypertensives than in normotensives. The results could not be explained on the basis of a disturbance in hepatic blood flow and/or in the metabolic clearance rate of aldosterone. The study provided evidence that, in patients with sustained essential hypertension and equilibrated sodium balance, there is an excess of plasma aldosterone relative to the levels of extracellular fluid volume and plasma renin activity. The excess is probably related to an abnormality in the adren