Using spectrophotometric method, we studied the activities of serum alpha-L-fucosidase, N-acetyl-beta-D-glucosaminidase and alpha-D-mannosidase in 94 patients, of whom 32 had acute hepatitis, 4 subacute fulminant hepatitis, 27 chronic active hepatitis, 22 posthepatitic cirrhosis and 9 hepatocellular carcinoma. In comparison with normal controls, the activities of the three glycosidases in the patients were significantly increased. The degree of the elevation of alpha-L-fucosidase activity correlated to the clinical phases and the course of acute infection of hepatitis B virus (HBV). The levels of glycosidase activities could reflect to a certain degree the pathological variations of the liver. Monitoring the levels of glycosidase activities, especially alpha-L-fucosidase, would be helpful in the diagnosis and medical care of viral hepatitis and hepatocellular carcinoma.