Three hundred and eighty male hypertensive patients with diastolic blood pressures averaging 90 to 114 mm Hg were randomly assigned to either active antihypertensive agents or placebos. The estimated risk of developing a morbid event over a five-year period was reduced from 55% to 18% by treatment. Terminating morbid events occurred in 35 patients of the control group as compared to 9 patients in the treated group. Nineteen deaths related to hypertension or atherosclerosis occurred in the control group and 8 in the actively treated group. In addition to morbid events, 20 control patients developed persistent diastolic levels of 125 mm Hg or higher. Treatment was more effective in preventing congestive heart failure and stroke than in preventing the complications of coronary artery disease. The degree of benefit was related to the level of prerandomization blood pressure.