A comparative study using hydrazinolysis has revealed that the oligosaccharide pattern of gamma-glutamyltranspeptidase purified from rat AH-66 hepatoma cells is very different from that of the enzyme from rat liver. Studies of oligosaccharides in each fraction have clarified the structural basis of the difference found in the sugar chains of the two enzymes. The sugar chains of the liver enzyme were all acidic, while 28% of those of the hepatoma enzyme were neutral, the latter being composed of high-man-nose-type and complex-type sugar chains. Three prominent structural differences were found in the acidic sugar chains of the two enzymes: (a) the sugar chains of the liver enzyme have complete outer chains, Gal beta 1 leads to 4GlcNAc beta 1 leads to, while many of those of the hepatoma enzyme have incomplete outer chains without galactose (Gal); (b) the Gal beta 1 leads to 4GlcNAc beta 1 leads to Gal beta 1 leads to 4GlcNAc beta 1 leads to group is found in the sugar chains of the liver enzyme but not in those of the hepatoma enzyme; (c) more than 40% of the sugar chains of the hepatoma enzyme contain bisect N-acetylglucosamine (GlcNAc) residue which is not found in those of the liver enzyme. Furthermore, the total number of asparagine-linked sugar chains in one molecule of hepatoma enzyme was about 4 times that found in one molecule of liver enzyme.