Cereal grain diets a †ect serum lipids by their soluble Ðbre and tocotrienols. Chickens were fed diets containing an oat bran fraction or waxy hulless barley that were enriched or depleted in b-glucan and/or tocotrienols. Serum cholesterol and triacylglycerides and enzymes of cholesterol metabolism were measured. Weight gains appeared to be lower in birds on oat bran fractioncontaining diets and higher in those on barley-containing diets supplemented with b-glucanase. All diets containing oat bran fraction or barley lowered serum total cholesterol and low-density-lipoprotein (LDL) cholesterol relative to the corn control diet. LDL cholesterol was reduced more by oat bran fraction supplemented with tocotrienols than by either oat bran fraction or tocotrienols alone. LDL cholesterol levels were the same for all barley-based diets. Activities of b-hydroxy-b-methylglutaryl coenzyme A (HMG CoA) reductase and cholesterol 7a-hydroxylase were inversely a †ected by the diets. Oat bran fraction plus tocotrienols, barley and solvent-extracted barley decreased HMG CoA reductase by 50% and increased cholesterol 7a-hydroxylase by 100% ; other diets caused lesser e †ects. It was concluded that both b-glucan and tocotrienols a †ected cholesterol levels and metabolism, and the e †ects were additive or less. Removal of b-glucan from barley diets abolished or diminished e †ects on enzyme activities but did not alter e †ects on cholesterol levels, indicating the possibility of another component in barley that a †ected cholesterol levels.