A total of 841 healthy men and women aged 25 to 49 years, with diastolic blood pressures of 78 to 89 mm Hg, were randomly assigned to a control treatment group (no dietary counseling) or to one of four dietary counseling treatment groups (reduced calories, reduced sodium, reduced sodium and calories, or reduced sodium and increased potassium). Participants were followed for a 3-year period to assess the effect of dietary changes on blood pressure. After 6 months, counseling had resulted in a net (of control) mean overnight urinary sodium reduction of 13%, a potassium increase of 8%, and a decrease in mean body weight of 7%. At 3 years, the sodium and weight reductions were 10% and 4%, respectively; the potassium change was nil. All four dietary counseling treatment groups had lower mean blood pressures than the control group. The largest net reduction in blood pressure occurred in the calorie group: diastolic pressure was 2.8 mm Hg and 1.8 mm Hg and systolic pressure, 5.1 mm Hg and 2.4 mm Hg at 6 months and 3 years, respectively. All four dietary counseling treatment groups experienced fewer hypertensive events; significantly fewer occurred in the sodium groups. The beneficial effects on blood pressure achieved in this trial have implications for the prevention of cardiovascular disease through dietary reduction of calories and sodium.