Sixty-one men with known hypercholesterolemia (plasma cholesterol greater than 265 mg/dl), most of whom were previous participants in the Coronary Primary Prevention Trial of the U.S. Lipid Research Clinic Program, were chosen to take part in this study to test the effectiveness of a new low-calorie (Questran Light) cholestyramine formulation against the proven effectiveness of the currently marketed formulation Questran in maintaining lowered plasma cholesterol levels. The study recorded changes in fasting plasma lipids, total cholesterol, high-density lipoprotein cholesterol, triglycerides, and calculated low-density lipoprotein cholesterol. After establishing baseline lipid/lipoprotein levels in a 3-week period during which all participants received the currently marketed formulation, the men were randomized into 2 groups, 1 group (n = 31) taking the new Questran Light formulation of 4 g of cholestyramine in 5 g of powder per pack, while the other group (n = 30) continued to take the marketed Questran formulation of 4 g of cholestyramine in 9 g of powder per pack. Each group consumed a total of 24 g/day of cholestyramine in 2 divided doses. At the end of the maintenance phase of the study there were no statistically significant mean changes in percentage from baseline to end-point lipid/lipoprotein levels within either group, nor were there any significant differences between the Questran Light group or the currently marketed Questran formulation group. The new low-calorie cholestyramine formulation appears to be equally as effective in maintaining lowered plasma cholesterol levels as the currently marketed formulation.