1. The diurnal excretion of sodium and potassium was observed in young people, with and without a genetic predisposition to hypertension, both in the presence and absence of psychological stress.
2. In the absence of stress, the normal day/night sodium excretion ratio was reversed in the children of hypertensive parents. This was significantly less than day/night sodium excretion in children of normotensive parents. A similar finding was observed for day/night potassium excretion.
3. There was a significant negative correlation between systolic blood pressure and day/night sodium excretion in children of hypertensive parents but not in children of normotensive parents.
4. After the mental stress of a University examination day/night sodium reverted to normal in children of hypertensive parents.