The serum total, free esterified and (LDL + VLDL)-cholesterol levels of rats maintained on a 10% refined rice bran oil diet were significantly lower than those on a 10% groundnut oil diet; HDL-cholesterol showed a tendency to be higher. Addition of oryzanol at 0.5% level to the diet containing rice bran oil showed a further significant decrease in serum total cholesterol. Liver lipids of rats fed bran oil were also markedly lower than their groundnut oil fed counterparts. Though the liver lipids of rats fed oryzanol along with RBO showed a further lowering, it was not statistically significant. The cholesterol lowering ability of rice bran oil appears to be due to oryzanol and to some other components of the unsaponifiable matter.