Two hundred and one volunteers with no known hypertension and 60 patients with untreated hypertension were entered into a study that compared the effect of two levels of sodium intake on blood pressure. One hundred and fifty-four volunteers and 46 hypertensive patients reached compliance goals, with a urinary sodium excretion on the high sodium diet twice that on the reduced sodium intake. The blood pressure on the high sodium diet was 4.5 +/- 0.5 mmHg (n = 154 p less than 0.001) higher than on the reduced sodium diet in normotensive individuals and was increased by 8.4 +/- 1.5 mmHg (n = 46 p less than 0.001) in hypertensive individuals. In the volunteer group the major rise in blood pressure occurred in people over the age of 50. In the hypertensive patients the alteration in blood pressure was not age dependent. In the younger age groups some individuals had an increase in blood pressure when on the high sodium intake which was outside the spontaneous variations in blood pressure of a control group. This implied that a number of young normotensive individuals were susceptible to this alteration in sodium intake. Changes in sodium intake alter blood pressure in hypertensive people, in normotensive people over 50 and in a small number of younger normotensive people. Overall reduction of sodium intake from 200 - 70 mmol/day would reduce the blood pressure level of the population and would reduce the number of people who have a blood pressure that requires drug therapy.