The hypocholesterolemic effects of oat bran (OB) have been recently challenged. To carefully document the hypocholesterolemic effects of OB, 20 hypercholesterolemic men admitted to a metabolic ward were randomly allocated to either OB or wheat bran (WB) for 21 d after a 7-d control-diet period. Control and treatment diets were designed to be identical in energy content and nutrients, differing only in the amount of soluble fiber. After 21 d, OB significantly decreased total cholesterol by 12.8% (P less than 0.001), low-density-lipoprotein cholesterol by 12.1% (P less than 0.004), and apolipoprotein B-100 by 13.7% (P less than 0.001) whereas WB had no significant effect. High-density-lipoprotein cholesterol and apolipoprotein A-I did not change significantly in either group. Serum triglycerides decreased by 10% in both groups but the decrease was only significant (P less than 0.04) in WB subjects. OB but not WB significantly reduced total cholesterol and other atherogenic lipoprotein fractions independent of other dietary changes.