Scientific studies support recommendations to increase dietary soluble fiber as part of hyperlipidemia treatment. Rice bran contains minimal soluble fiber, but rice bran oil has a hypolipidemic effect. Full-fat rice bran was compared with oat bran and a rice starch placebo in hyperlipidemic humans to see if it might have a role in the treatment of hyperlipidemia. Moderately hypercholesterolemic (5.95-8.02 mmol/L), nonsmoking, nonobese adults were studied in a 6-wk, randomized, double-blind, noncross-over trial. Three groups added 84 g/d of a heat-stabilized, full-fat, medium-grain rice bran product (n = 14), oat bran product (n = 13) or rice starch placebo (n = 17) to their usual low-fat diet. Serum cholesterol, triglycerides, HDL-cholesterol (HDL-C), LDL-cholesterol (LDL-C), apoA1 and apoB were measured before and at the end of the supplementation period. Serum cholesterol decreased significantly (P </= 0.05) by 8.3 +/- 2.4% and 13.0 +/- 1.8% in the rice bran and oat bran groups, respectively, but there was no change in the rice starch group. This change was attributable to LDL-C, which decreased by 13.7 +/- 2.8% in the rice bran group and 17.1 +/- 2.4% in the oat bran group (P </= 0.05). Serum apoB decreased proportionately. There was no consistent effect on triglycerides within each group and HDL-C and apoA concentrations did not change. The LDL-C:HDL-C ratio decreased significantly in the rice bran and oat bran groups. Stabilized, full-fat rice bran or oat bran, added to the prudent diet of hyperlipidemic adults, similarly reduced cholesterol and LDL-C and improved lipid ratios in 78% of these individuals. Rice bran, as well as oat bran, should be included in the prudent diet of individuals with hyperlipidemia.