We investigated 56 patients with stage II essential arterial hypertension (EAH) and 18 healthy volunteers. To determine the blood pressure (BP) salt-reactivity types we used dietary protocol. We studied renal natriuresis with clearance tests. Salt-resistant EAH was characterized by preserved renal natriuresis, therefore high-salt diet did not cause extracellular fluid retention and hypertensive reaction. Salt-sensitive EAH was characterized by impaired renal natriuresis under high-salt diet that caused increased glomerular filtration and sodium reabsorbing in the proximal tubules. As a result, extracellular fluid retention, hypervolemia and hypertensive reaction appeared in this group. EAH with paradoxical BP reactivity was characterized by increased renal natriuresis in the low-salt diet because of decreased sodium reabsorbing in the proximal and distal tubules. In spite of the glomerular filtration reduction, extracellular fluid volume was decreased and hypovolemia with hypertensive reaction appeared. The high-salt diet restored natriuresis, extracellular fluid volume and BP level in patients of this group.