Our results showed that alpha-asarone was an inhibitor of hepatic HMG-CoA reductase and that the administration of alpha-asarone at 80 mg/kg body wt. for 8 days decreased serum cholesterol by 38% (p < 0.001) in hypercholesterolemic rats. This alpha-asarone treatment affected mainly the serum LDL-cholesterol levels, leaving serum HDL-cholesterol lipoproteins unaffected, with a consequent decrease of 74% in the LDL/HDL ratio. In addition, alpha-asarone especially stimulated bile flow in hypercholesterolemic rats (60%), increasing the secretion of bile salts, phospholipids and bile cholesterol. The drug also reduced the cholesterol levels of gallbladder bile, whereas the concentration of phospholipids and bile salts increased only slightly, leading to a decrease in the cholesterol saturation index (CSI) of bile in the hypercholesterolemic rats. This CSI decrease and the increase in bile flow induced by alpha-asarone may account for the cholelitholytic effect of alpha-asarone. It seems that alpha-asarone induced clearance of cholesterol from the bloodstream and that the excess of hepatic cholesterol provided by LDL-cholesterol is diverted to bile sterol secretion via a bile choleresis process. The inhibition of HMG-CoA reductase and the increase in bile flow induced by alpha-asarone, as well as the decrease in the CSI, could then explain the hypocholesterolemic and cholelitholytic effects of alpha-asarone.