Hypolipidemic effects of the usual gamma-oryzanol (gamma-OZ) and a new gamma-OZ (N-gamma-OZ) with a different sterol composition from gamma-OZ were investigated on the hyperlipidemia induced by ingestion of a high cholesterol diet (HCD) containing 1% cholesterol for 12 days in male Sprague-Dawley rats. Treatment with gamma-OZ for 6 days significantly inhibited the increase in serum total cholesterol (TC) and phospholipids (PL) induced by HCD, while the treatment with gamma-OZ for 12 days did not inhibit the increase of TC and PL. Treatment with N-gamma-OZ at 100 or 1000 mg/kg for 6 days slightly inhibited the increase of TC by HCD. The decrease of TC in high density lipoprotein (HDL-TC) was markedly inhibited by treatment with N-gamma-OZ for 12 days, but N-gamma-OZ for 6 days and gamma-OZ for 6 and 12 days did not inhibit the decrease of HDL-TC. Treatment with N-gamma-OZ for 12 days significantly inhibited the increase of PL and free cholesterol (FC) by HCD. gamma-OZ at 1000 mg/kg for 12 days also inhibited the increase of FC. N-gamma-OZ significantly reduced the atherogenic index using TC and HDL-TC by affecting the HDL-TC increase. gamma-OZ at 100 mg/kg and N-gamma-OZ at 100 mg/kg for 6 days reduced the atherogenic index using TC and HDL-TC by the inhibition of TC increase. The atherogenic index using PL and HDL-PL was only reduced by the treatment with N-gamma-OZ at 1000 mg/g for 12 days. The increase of triglyceride (TG) by HCD was inhibited by the treatment of N-gamma-OZ for 6 days (all doses) and 12 days (500, 1000 mg/kg), and gamma-OZ at 500 mg/kg for 6 and 12 days also inhibited the increase of TG by HCD. gamma-OZ and N-gamma-OZ had no effects on liver lipid contents. The hypolipidemic effect of N-gamma-OZ was slightly more potent than that of gamma-OZ.(ABSTRACT TRUNCATED AT 250 WORDS)