1. Whole-body elimination rate of 22Na+ was decreased in normotensive or borderline first-degree relatives of hypertensive probands.
2. Whole-body potassium; exchangeable sodium and urine excretion of sodium, potassium and creatinine were similar in relatives and controls.
3. Erythrocyte net influx of 22Na+ was significantly increased in normotensive relatives.
4. Abnormal whole-body and cellular handling of sodium (22Na+) demonstrated in relatives indicates that this abnormality may have an important role in the development of essential hypertension in man.