Glycosaminoglycan, a component of connective tissue, increased significantly in tissue fibrosis including liver cirrhosis. It has been reported that N-acetyl-0-D- glucosaminidase takes place important role in tissue fibrosis and that the degree of fibrosis is reflected in serum N-acetyl- β -D-glucosaminidase activity in hepatic fibrosis. Morevoer, in tissue fibrosis collagen formation is the main event. And in Collagen formation monoamine oxidase has function of fixation of the soluble collagen molecule and of stimulation of the connective tissue maturation. It also has been reported that serum monoamine oxidase activity reflects hepatic monoamine oxidase activity and the activity is related to the synthetic activity more than the accumulated amount of the collagen. The authors have investigated the activities of N- acetyl-β-D-glucosaminidase and monomaine oxidase in the serum in 15 healthy subjects and 55 patients with various liver diseases. In patients with chronic hepatitis, liver cirrhosis and hepatoma, serum N-acetyl- β -D-glucosaminidase activity increased twice as the value of healthy subjects. Serum monomaine oxidase increased significantly in chronic hepatitis (p<0.001) and liver cirrhosis (p<0.01). No definite correlation was found between any of liver function tests or the evidence of protal hypertention and these two enzyme activities on patients with liver cirrhosis. These results suggest that serum N-acetyl- β -D- glucosaminidase and monomamine oxidase activities can be used as an important index in the evaluation of the hepatic fibrogenesis and its therapy.