Cardiac output, plasma and blood volume were studied in 180 patients with essential hypertension via the method of dye dilution and neuro-hormonal studies were realized. In part of tha patients observed, the plasma renin activity and plasma aldosterone were established by radioimmune methods. The values of sodium in plasma and its excretion with urine were determines. Aldosterone and plasma sodium in the circulating blood volume were determined by methods, introduced by the author. Three subgroups of patients were differentiated on the base of the changes in sodium metabolism: with elevated sodium in plasma, with normal values of plasma sodium and with reduced sodium content in the circulating plasma volume. The changes in plasma sodium of the subgroups of patients with essential hypertension are accompanied by certain deviations in hemodynamics, in plasma aldosterone and in plasma renin activity.