Significant reductions of plasma cholesterol can be effected in most patients with hypercholesterolemia by interruption of the enterohepatic circulation of bile acids. This can be accomplished medically by the use of cholestyramine resin, or surgically by the ileal exclusion operation. Both procedures cause a block in the reabsorption of bile acids. Due to release of feedback regulation from a reduction in bile acids returning to the liver, the conversion of cholesterol into bile acids is greatly enhanced; this in turn causes a drain on body cholesterol. A decrease in the plasma cholesterol level is one consequence of this change and, in many patients, large reductions of cholesterol can be achieved. Although these approaches to the treatment of hypercholesterolemia are associated with certain gastrointestinal side effects, both cholestyramine and ileal exclusion represent promising methods for treatment of this disorder.