Abstract: The serum level of immunologic-changed CuZn-containing superoxidant dismutase （GuZn-SOD） was determined in 41 patients with lung cancer and compared with that in 22 normal persons and 11 cases of benign pulmonary disease.The following results were obtained: the X±SD in lung cancer was 16.20±5.41ng/ml; that in benign pulmonary disease was 9.32±4.29ng/ml; and that in normal adults was 7.22±3.72ng/ ml. The mean of the activity of serum immunologic-changed CuZn-SOD in patients with lung cancer was significantly higher （P＜0.001）. The serum immunologic-changed CuZn-SOD level （11.98ng/ml） may be served as a positive, finding for the presence of lung cancer, the positive rates being 78%,18%,4.5% in the three groups respectively.In the light of the above findings, it may be suggested that the determination of the activity of serum immunologic-changed CuZn-SOD is helpful in the diagnosis of lung cancer.