2,4,5-trimethoxycinnamic acid (TMC), the major and non toxic metabolite of a-asarone (2,4,5-trimethoxy-1-propenyl benzene), retains most of the pharmacological properties of a-asarone, since both substances, administered to hypercholesterolemic rats at 80 mg/kg body wt, decreased total serum cholesterol, lowered LDL-cholesterol levels and kept unaffected HDL-cholesterol levels. In addition, both substances increased bile flow, especially in hypercholesterolemic rats, by rising the secretion of bile salts, phospholipids and bile cholesterol. These drugs also reduced cholesterol levels of gallbladder bile, whereas phospholipids and bile salts concentrations were increased, decreasing the cholesterol saturation index (CSI). We also found that a-asarone was 20 times better inhibitor of HMG-CoA reductase than TMC. This effect on HMG-CoA reductase was the only property highly reduced in TMC in comparison with a-asarone, while the other pharmacological properties of a-asarone were retained by TMC. These experiments strongly suggest that TMC can be further studied as a possible hypocholesterolemic and cholelitholytic agent.