Sitostanol (24-ethyl-5 alpha-cholestan-3 beta-ol), a hydrogenated derivative of sitosterol, was administered in a low dose (1.5 g/day) for 4 weeks to 6 patients with hypercholesterolemia. Total cholesterol was reduced significantly after 3 and 4 weeks by 10 and 15%, respectively. The reduction of total cholesterol was entirely due to a fall in LDL cholesterol. Total triglycerides and HDL cholesterol were not altered. Two weeks after cessation of sitostanol administration serum cholesterol returned to pretreatment levels. No significant amounts of sitostanol could be detected in plasma during therapy. These results suggest that low-dose sitostanol might be a useful hypolipidemic agent for the treatment of mild hypercholesterolemia.