The effects of grape seed polyphenol (GSP) administered orally at doses of 0.01-1.0 g/kg per day to normal and hypercholesterolemic rats for 28 and 36 days, respectively, was evaluated by measuring changes both in the concentrations of serum and hepatic lipids and in fecal steroid excretion. Body weight gain decreased dose-dependently both in normal and hypercholesterolemic rats. Relative weight of the liver was significantly lower in normal rats given more than 0.2 g/kg GSP compared with control rats. Compared with control groups, relative weight of the liver was significantly lower in normal rats given more than 0.2 g/kg GSP, and in hypercholesterolemic rats given more than 0.1 g/kg GSP, respectively. In hypercholesterolemic rats, food or calorie intake was significantly lower in rats given more than 0.1 g/kg GSP than in control rats. Dose-dependency was observed in serum concentrations of serum triglycerides and thiobarbituric acid reactive substances and the content of hepatic phospholipids in normal rats, and in serum concentration and hepatic content of triglycerides in hypercholesterolemic rats. A significant increase in fecal excretions of neutral steroids and bile acids was found in normal rats given a dose of 1.0 g/kg GSP. Dose-dependent decrease of 12-keto lithocholic acid and increase of lithocholic acid were also observed. By contrast, there was no significant change in fecal excretions of neutral steroids and bile acids in hypercholesterolemic rats. Thus, GSP seems to affect lipid metabolism in rats by lowering the concentrations of serum and hepatic triglycerides rather than by altering the metabolism of cholesterol.