The Multicenter Isradipine/Diuretic Atherosclerosis Study (MIDAS) is a double-blind, randomized, controlled clinical trial comparing the effects of isradipine and hydrochlorothiazide on the progression or regression of early carotid atherosclerosis in 883 hypertensive patients. Assessment of the outcome is by B-mode ultrasonographic measurement of early lesions (as reflected by intimal-medial wall thickening) at baseline and semiannually over 36 months. At baseline, the participants' mean age was 58.5 years. The study population was 78.6% male and 72.4% white. The average resting systolic and diastolic blood pressures were 149.8 and 96.5 mm Hg, respectively. Mean total serum cholesterol and low-density lipoprotein (LDL)-cholesterol levels were 216.2 mg/dL and 146.6 mg/dL, respectively. Risk factors for coronary artery disease were balanced at baseline between the two study groups. The mean maximum intimal-medial thickness at baseline (measured in the near and far walls of three segments for both carotid arteries) was 1.17 +/- 0.20 mm; the mean intimal-medial thickness of the single thickest lesion was 2.11 +/- 0.51 mm. Cross-sectional analyses show that intimal-medial thickness correlates independently with male gender, age, number of cigarettes smoked per day, levels of LDL cholesterol, systolic blood pressure, and white blood cell count. The MIDAS endpoint results will be available in 1993.