Pravastatin was administered to 20 patients with hyperlipidemia type IIa and IIb, for a period of 8 to 16 weeks at a daily dose of 10 to 20 mg, to investigate the effects on serum and biliary lipids. At the end of the treatment with pravastatin, the serum cholesterol level was significantly reduced, by 20%, compared with the control level. On the other hand, no significant differences were observed in serum high-density lipoprotein (HDL) cholesterol and triglyceride levels. Additionally, the administration of pravastatin did not change mode % compositions of biliary lipids, such as cholesterol, phospholipids, and total bile acids, as well as individual biliary bile acids. Consequently, there was not any significant change of the cholesterol saturation index. Based on the above results, our findings suggest that, for the treatment of hyperlipidemia, pravastatin is a highly effective cholesterol-lowering drug that does not affect biliary lipid metabolism.