The Multicenter Isradipine/Diuretic Atherosclerosis Study (MIDAS) is a randomized, double-blind, active-control trial to compare the effectiveness of two treatment regimens for the control of hypertension in reducing the rate of progression of early extracranial carotid artery atherosclerosis in hypertensive patients. The two double-blind treatment regimens are 2.5 or 5 mg isradipine twice daily and 12.5 mg or 25 mg hydrochlorothiazide twice daily. Patients whose blood pressure is not controlled with either of these regimens will receive, in addition to the highest tolerated dose of the blinded drug, 2.5 to 10 mg open-label enalapril twice daily. The MIDAS study has enrolled 883 patients to treatment with either isradipine or hydrochlorothiazide. Inclusion criteria included men and women over the age of 40 years, the presence of an atherosclerotic lesion in the extracranial carotid artery demonstrated on B-mode ultrasound scanning (maximum thickness between 1.3 and 3.5 mm), an average sitting diastolic blood pressure between 90 and 115 mm Hg, and low-density lipoprotein levels between 130 and 189 mg/dL. An assessment of each patient's blood pressure and any side effects is made every three months; a B-mode ultrasound examination of the carotid arteries was performed at baseline and every six months thereafter; an electrocardiogram was carried out at baseline and once a year thereafter; and a brief quality-of-life assessment was made at baseline and every year thereafter.