γ-Glutamyl(acyltransferase (γ-GT) is widely distributed in human tissues, most in the kidney, followed by the pancreas and liver, and most in the liver during the embryonic stage, and in the liver mainly in the hepatocyte plasma and intrahepatic bile duct epithelium. γ-GT in normal human serum is mainly from the liver. γ-GT has some clinical value for various hepatobiliary diseases. In most hepatobiliary diseases, its activity is elevated, but the relative ratio of its elevation to other serum enzyme activities varies in different hepatobiliary diseases: (1) In patients with primary or metastatic hepatocellular carcinoma, most of this enzyme is moderately or highly increased, which can be several times or even tens of times greater than normal, while other systemic tumors are mostly normal. However, the measurement results of GGT in hepatocellular carcinoma overlap a lot with other hepatobiliary diseases, especially with jaundice. Therefore, the measurement of GGT alone has no diagnostic value for hepatocellular carcinoma, but if methemoglobin, AKP and GGT are measured simultaneously, the diagnostic value is greater (if methemoglobin is negative, but AKP and GGT are increasing, especially if there is no jaundice and transaminases are normal or only mildly elevated, the possibility of hepatocellular carcinoma should be highly alerted). (2) In intrahepatic or extrahepatic bile duct obstruction, GGT excretion is blocked and returns to the blood with bile, resulting in a rise in serum GGT. (3) In acute viral hepatitis, hepatocytes adjacent to the necrotic area have hyper-synthesis of chymotrypsin, causing an increase in serum GGT. (4) In chronic active hepatitis, GGT is often 1 to 2 times higher than normal, and if it is elevated for a long time, there may be a tendency of liver necrosis. (5) In cirrhosis, the change of serum GGT depends on the activity of intrahepatic lesions and their etiology. It is mostly normal in the inactive phase, but tends to rise if accompanied by inflammation and progressive fibrosis. In primary or secondary biliary cirrhosis, there is often an early elevation of GGT. It is believed that GGT is elevated in the early stage of cirrhosis, but is low in severe patients, especially in advanced cases, probably due to the loss of hepatocyte GGT synthesis ability, thus it is believed that patients with cirrhosis have high GGT, suggesting that the disease is still in the early stage. (6) In patients with fatty liver, GGT is also often elevated, but in general, most of the serum GGT activity in nutritional fatty liver does not exceed two times the normal value. (7) In patients with alcoholic hepatitis and alcoholic cirrhosis, GGT is almost always elevated, which becomes an important feature of alcoholic liver disease.