Maintenance of cholesterol balance under many conditions affecting rate of synthesis implies that control of cholesterol metabolism is related to turnover rate, rather than biosynthesis only. In this study, cholesterol biosynthesis was manipulated by drugs and rate of incorporation of acetate and rate of excretion of 4- 14C-sterol nucleus were measured. Rats were given a bile acid binding polymer (cholestyramine) in the diet, an inhibitor of cholesterol biosynthesis (triiodothyropropionic acid), or both for varying lengths of time. Results indicate that cholesterol balance is maintained under the conditions studied. It appears that extrahepatic processes contribute substantially to maintenance of cholesterol balance.