BACKGROUND To characterize the possible existence of kinetic anomalies of four erythrocyte membrane sodium transport systems in a group of essential hypertensive patients, and to study the clinical and biochemical profile of those with anomalies. METHODS We studied 33 essential hypertensive patients and 33 normotensive controls. The kinetics (maximal rate and apparent dissociation constant for internal sodium) of Na(+)-K+ pump, Na(+)-K(+)-Cl- cotransport and Na(+)-Li+ countertransport was calculated after a sodium loading procedure, according to the methods of Garay; the passive Na+ permeability was also determined. RESULTS The studied kinetic parameters were not significantly different in both groups. Nevertheless, we found a group of hypertensive patients with some transport abnormalities: increased intracellular sodium (9.1%), accelerated Na+ passive permeability (9.1%), lower activity of the Na(+)-K+ pump (7.1%) and the Na(+)-K(+)-Cl- cotransport (4%) and an increased maximal rate of the Na(+)-Li+ countertransport (11.8%). Na+Li+ countertransport activity was statistically related to plasma levels of urea, creatinine, glucose and LDL-cholesterol, and the activity of the Na(+)-K(+)-Cl- cotransport was related to plasma uric acid. The hypertensive patients with sodium transport anomalies showed higher body mass index, uric acid plasma levels and atherogenic index than those without these kind of anomalies, and they also showed lowered HDL-cholesterol plasma levels. CONCLUSIONS A small group of essential hypertensive patients (around 31%) show kinetic alterations of sodium transport systems. There is a relation between Na(+)-Li+ countertransport activity and some cardiovascular risk parameters. Hypertensive patients with transport anomalies are a group with an increased cardiovascular risk.