1. Erythrocyte Na+-K+ cotransport and Na+-Li+ countertransport were measured at the same time in 56 essential hypertensive patients, 24 of their normotensive offspring and 36 matched normotensive controls.
2. The mean value of Na+-K+ cotransport is slower and of Na+-Li+ countertransport is faster in the essential hypertensive group and in some of their normotensive offspring, but a great overlap with the value of the normotensive group was observed.
3. Na+-K+ cotransport values were bimodally distributed in the hypertensive group, with the first mode at 250 and the second at 600 μmol h−1 l−1 of erythrocytes.
4. The ratio Na+-K+ cotransport/Na+-Li+ countertransport was calculated. It was found that such a ratio distinguishes between normotensive and essential hypertensive subjects better than the individual transport systems alone.
