To the Editor.—Cooper et al<sup>1</sup>have recently reviewed the variations and practical utility of blood lipid measurements and have suggested that oat bran has only a modest cholesterol-lowering effect, and that dietary fiber grain supplements reduce cholesterol levels mainly because they replace dietary saturated fats. They base their conclusions primarily on a publication by Swain et al<sup>2</sup>; however, additional studies have since examined the relationships between dietary fiber, diet, and blood lipids, and have concluded that the cholesterol-lowering effects of fiber are not strictly a function of dietary substitution.<sup>3-5</sup> Anderson et al<sup>3</sup>studied 20 hypercholesterolemic men in the metabolic ward who were randomly allocated to either oat bran or wheat bran for 21 days after a 7-day control-diet period. Control and treatment diets were designed to be identical in energy content and nutrients, and differed only in the amount of soluble fiber. Oat bran significantly decreased