Abstract: The Serum y-glutamyl transpeptidase isoenzyme (y---GT isoenzyme) were assay- ed in 59 patients with Primary liver cancer or other Space-occupying lesions.The serum AFP concentration of all patients were less than 400ng/ml, Using 4~ 30% Polyacrylamide gradient gel electrophoresis, it was found that band I'、II'、III of y-GT isoenzyme were specific for primary liver cancer (PLC).One or more specific bands were presented in 66,7% of the patients with PLC, in62,5% of thePatients.with small PLC, No Specific bands were presented i.n patients with benign liner lesion,we concluded that y-GT isoensyme may be a specific tumor markern of PLC.