Abstract: Objective: To study the clinical significance on plasma glutathione S tranceferase （GST-π） level in patients with lung cancer.Methods: The plasma levels of GST-π were measured by RIA in 58 lung cancer patients and 139 healthy adults served as control. Results: The plasma GST-π levels elevated above a cut off value of 13.35μg/L in 43 of the 58 patients （mean ± 1.96 standard deviations in 139 healthy control subjects）. Plasma levels of GST-π reduced greatly after operation. But no correlations were noted among GST-π level, pathological type, histological differentiation and TNM stage （P＞0.05）. And there were no significant differences for pre or post chemotherapy. The mean pretreatment GST-π level was significantly lower in patients with a partial responce to chemotherapy than those with no response.Conclusion: The plasma GST-π level may be a valuable tumor marker and may help to avaluate operation effect for lung cancer. Interestingly, pre treatment plams GST-π level seems to be a useful indicator for predicting therapeutic response to combination chemotherapy regiments including platinum compound in lung cancer.