A comparison was made of the physicochemical characteristics of erythrocyte membranes in two strains of spontaneously hypertensive rats, namely SHR and MHS and in patients with essential hypertension (EH). The authors confirmed the results of the previously reported studies that Na+/Li+/H+ countertransport rates were higher in the erythrocytes of patients with EH. The high rate of L1+ sodium-independent efflux hindered identification of Na+/H+ turnover in the rat erythrocytes. Na+/H+ turnover rate was higher in SHR and unchanged MHS rat erythrocytes. The rate of Na+/K+ countertransport was increased by 30-50% in SHR rats and by 90-110% in MHS rats as compared with control animals of respective lines. No difference was found in this parameter in EH patients. The erythrocytes from EH patients and SHR rats showed a higher sensitivity of their K+ channels to elevated intracellular calcium levels. This parameter was unaltered in MHS rats. In the red cells of MHS rats there was a 4-5-fold increase in hemolysis which was induced by higher intracellular calcium concentrations, which was associated with increased activity of a Ca2+-dependent form of protease. The level of Ca2+-induced hemolysis remained unchanged in the erythrocytes from SHR rats and EH patients. It has been concluded that, in terms of membrane abnormalities, in SHR rats are the most adequate model of human essential hypertension than are MHS rats.