The activity of the sympathoadrenal and renin-angiotensin-aldosterone systems was studied in patients with myocardial infarction complicated by cardiogenic shock. During the initial 12 hours after the onset of myocardial infarction an increased plasma level of adrenalin and noradrenal is observed, which then returns to the normal level on the 3rd day. In cases of cardiogenic shock a lower content of catecholamines in blood is noted. The determinations of renin activity in the plasma of peripheral venous blood demonstrated that it was increased since the 1st day of the disease in the myocardial infarction patients, but that its maximum elevation fell within the 7th--10th days. In patients with cardiogenic shock the plasma renin activity was much higher than in those with uncomplicated myocardial infarction. Urine aldosterone excretion was higher in patients with cardiogenick shock since the 1st day of the disease than in those with an uncomplicated course of myocardial infarction. The study of the electrolyte balance in patients with myocardial infarction complicated by cardiogenic shock demonstrated that on the 1st day of the disease the potassium level in plasma and erythrocytes was decreased, while the sodium concentration was somewhat increased.