The Lipid Research Clinics Coronary Primary Prevention Trial and the Coronary Drug Project had shown that morbidity and mortality from ischemic heart disease were reduced by blood cholesterol-lowering therapy. Although blood cholesterol reduction ameliorated experimental atherosclerosis in animal models, the two largest human studies with angiographic observation of arterial lesion change, the NHLBI Type II Coronary Intervention Study and a study by Cohn et al, had not demonstrated significant treatment effects. Favorable, but inconclusive, treatment trends were observed in four unrandomized angiographic trials and one trial too small for evaluation of randomized groups.