Forty-eight people with hypertension entered a controlled study to observe the effect of sodium (NaCl) restriction on blood pressure. In people with mild hypertension (diastolic blood pressure 90-105 mmHg), sodium restriction reduced blood pressure compared with a control group and 75% obtained a diastolic blood pressure of less than 90 mmHg. In people with more severe hypertension (diastolic blood pressure 4105 mmHg), sodium restriction achieved the same level of control as chlorothiazide (500 mg a day). Restriction of sodium intake is an effective method of reducing blood pressure and should be the first form of therapy in people with mild hypertension.