Dietary fiber lowers atherogenic serum lipids and blood pressure and improves glucose metabolism. We compared in 24 mildly hypercholesterolemic men the effects of adding 11.8 g dietary fiber/d from each of three cereal brans (wheat, rice, and oat) to a low-fiber diet for 4 wk each. A double-blind, crossover design incorporated brans into bread and muffins. Plasma total- and low-density-lipoprotein-cholesterol concentrations were significantly lowered only by oat bran. Compared with wheat bran, the ratios of plasma high-density-lipoprotein cholesterol to total cholesterol and of apolipoprotein A-I to B were significantly increased with oat bran (both by 4.7%, P less than 0.05), and rice bran (2.3%, P less than 0.05, and 3.9%, P less than 0.05, respectively). Blood pressure, blood glucose, and serum insulin responses to a common test meal were unaltered. Oat and rice bran exert a small but potentially useful effect on plasma lipoprotein risk factors for cardiovascular disease.