Using our ELISA kit for GST-alpha, we tested the serum GST-alpha levels of patients with hepatitis A, acute hepatitis B (HB), chronic active HB, chronic persistent HB and liver cirrhosis. Serum GST-alpha levels in all these groups of patients were significantly higher than those in the controls (P < 0.01). Serum GST-alpha levels was closely (P < 0.01) correlated with serum alanine transaminase (ALT) levels in various groups of patients except chronic persistant HB. The combined application of the two markers, GST-alpha and ALT, raised the sensitivity of detection for liver diseases. In detection of chronic persistent HB patients, the GST-alpha marker was more sensitive than ALT (P < 0.01). The follow-up data of GST-alpha and ALT markers in serum showed that the GST-alpha level could reflect the clinical progression of liver disease more exactly as observed in 79 liver cancer patients in then GST-alpha and ALT positive rate were 81% and 61% respectively (P < 0.01). In 30 persons with positive HBsAg, the positive rates of GST-alpha and ALT were 70% and 37%, respectively. These results indicated that, (1) the detection of GST-alpha combined with ALT was capable of increasing the sensitivity for recognizing hepatocellular damage; (2) the elevation of serum GST-alpha level mainly resulted from the increased expression of GST-alpha in liver cells during hepatocarcinogenesis, thus, the GST-alpha is thought to be a tumor marker for liver cancer; (3) GST-alpha measurement offers advantage over ALT for the detection of minor degree of hepatocellular damages. GST-alpha may act as an early, sensitive and specific enzyme marker.