1. The clinical applications of a simple laboratory test for the diagnosis of essential hypertension were further investigated on a large number of patients (124 individuals).
2. The reduced erythrocyte ratio of Na+/K+ net fluxes observed in essential hypertensives might be secondary to a functional defect in a Na+—K+ co-transport system.
3. A similar reduction in the ratio of Na+/K+ net fluxes was also observed in erythrocytes of some normotensive subjects born of hypertensive parents and of genetically hypertensive rats. This suggests that the erythrocyte membrane defect follows the genetic transmission of hypertension.