1. In normal young adult sons of normotensive parents the rate of renal sodium excretion is highly correlated with mean arterial pressure after a large intravenous isotonic fluid load. The correlation appeared to strengthen with time and was improved when the rate of sodium excretion was corrected for variations in the rate of glomerular filtration.
2. There was no such correlation in normal, age-matched sons of hypertensive parents.
3. In eight of the 20 normotensive sons of hypertensive parents studied, the rate of renal sodium excretion per unit of mean arterial pressure was significantly higher than in the sons of normotensive parents.
4. Because the sons of hypertensive parents are much more likely to become hypertensive than those of normotensive parents, we suggest that an abnormality of renal sodium handling precedes the development of demonstrable hypertension.