The authors measured Na(+)-H+ exchanger kinetics together with Na(+)-Li+ countertransport V(max) in the erythrocytes of 21 subjects with essential hypertension and 16 normotensive control subjects. Na(+)-H+ exchange V(max) appeared to be increased in patients with essential hypertension, while the Na(+)-H+ exchanger affinity for intracellular proton sites (K50%) proved to be unchanged and the index of cooperativity among intracellular proton binding sites as measured by Hill's coefficient (Hill's n) decreased as compared with normotensive control subjects. Na(+)-Li+ countertransport V(max) appeared to be higher in patients with essential hypertension than in control subjects. The authors were unable to find any correlations between Na(+)-H+ exchanger kinetic parameters and metabolic variables such as parameters of insulin resistance and plasma lipids. On the basis of the data obtained, erythrocyte Na(+)-H+ exchanger activity was found to be abnormal in two kinetic variables in essential hypertensive patients and showed no simple linear correlations with the main variables of glucose metabolism, plasma lipids, renin or aldosterone.