Plasma cholesterol esters are formed within the circulation by lecithin-cholesterol acyltransferase (LCAT), an enzyme produced by the liver. Patients with hepatocellular disease have low plasma LCAT activity. This largely accounts for the decreased levels of cholesterol esters observed in such patients and appears due to impaired hepatic production of the enzyme. In contrast, activity of the LCAT reaction in patients with cholestasis seems variable and is the subject of controversy, largely because the influence of abnormal cholestatic lipoproteins on the reaction requires further clarification.Human liver contains a lysosomal cholesterol ester hydrolase (CEH) which may play an important role in hepatic cholesterol homeostasis. In patients with liver damage there is no concrete evidence of circulating CEH activity, but recent studies show elevated activity of hydrolase within the liver itself in acute hepatitis. Hepatic activity of another lysosomal enzyme, acid phosphatase, is not increased, suggesting that high CEH in hepatitic liver does not simply reflect a general increase in lysosomal enzymes. The pathogenesis and significance of altered CEH activity in liver disease require further study.