Much circumstantial and some direct evidence links a high sodium, low potassium intake to the development of essential hypertension. However, studies to prove a definite causative relationship in man are unlikely to be done for the practical reason that they need to carried out over a whole generation. Restriction of sodium intake does lower blood pressure in many hypertensive subjects. This fall appears to be mediated in part by a diminished renin response to the sodium restriction as blood pressure becomes more severe. Less substantive evidence also suggests that increasing potassium intake may lower blood pressure but this effect seems to be more apparent when both animals and man are on a high intake. It would seem sensible, therefore, in the light of present knowledge, to advise communities that have a high sodium, low potassium diet they may benefit from a reduction in sodium and an increase in potassium intake. Patients who are already known to have high blood pressure should be advised to reduce sodium intake along with other non-pharmacological advice. In some patients this will be sufficient to control the blood pressure. In others who may then require drug treatment, the blood pressure lowering effect of beta-blockers and converting enzyme inhibitors will be enhanced by the sodium restriction.