Potassium metabolism was studied with the use of 42K nuclide in 68 patients with hypertensive disease, stage I-III (WHO classification) without signs of cardiac and renal insufficiency and in 13 persons of the control group, total body volume with tritium oxide dilution and central haemodynamics with radiocardiography were also recorded. Patients with the stable course of arterial hypertension show decreased potassium metabolism in the body, apparently with deterioration of the tissue metabolism. Decrease of the total metabolised potassium was seen in patients with hypertensive disease only in the sclerotic stage of illness, it is more marked in men than in women. Decrease of potassium content in the body did not depend on the duration and severity of arterial hypertension and on the changes in central haemodynamics. It is concluded that more information on total potassium content in the body is gained with calculated percentage to the predicted normal values in milliequivalents per liter of total water in the body.