CLAS-I was randomized and selectively-blinded. Screening for the trial consisted of five clinic visits, at which baseline data, including angiographic data, were obtained and a prerandomization trial of the study drugs was conducted. One hundred eighty-eighty subjects were randomized to either 30 grams (g) of colestipol hydrochloride plus 3 to 12 g of niacin daily or to placebo. Both groups received diet intervention. The drug group received less than 125 milligrams (mg) of cholesterol daily, 22 percent of energy as fat, 10 percent as polyunsaturated fat, and 4 percent as saturated fat. The placebo group received less than 250 mg of cholesterol per day, 26 percent of energy as fat, 10 percent as polyunsaturated fat, and 5 percent as saturated fat. The different diet composition for drug and placebo groups was to enhance the differential in blood cholesterol responses between the two groups. Study subjects and clinic staff were blinded to the prerandomization study drug trial lipid responses. Subjects were blinded to treatment assignments. Subjects and staff were not blinded to on-trial lipid values. The primary endpoint, the global change score, was change in atherosclerosis observed by angiography of native coronary arteries and aorta coronary bypass grafts. Evaluation of study end-points was performed by staff and consultants who were blinded to treatment group assignments, as well as to the temporal ordering of angiographic data. Subjects were seen monthly for the first six months and then at two-month intervals. A repeat angiogram was performed at two years. Of the 188 randomized subjects, 162 completed the study.