Abstract: Using luminescence immunoassay established by us, we have successfully made studies bn the antigen-antibody reaction between antibovine CuZn-SOD antisera and CuZn-SOD in the serum of malignant tumor patients.CuZn-SOD-I contents were found to be 0.43± 0.07ng/ml（X ±SE） in the serum of 210 healthy adults, whereas those were 8.98 ± 0.84, 5.71 ±0.90, 6.00 ± 1.24 and 7.68+2.10ng/ml in 41 cases of pulmonary carcinoma, 36 cases of hepatic carcinoma, 18 cases of mammary carcinoma and 11 cases of malignant obstructive jaundice respectively. The estimated values for malignant tumor were very significantly higher than those in healthy adults （P＜0.001） and also higher than those in patients with benign disease （P＜0.05）. It was worthwhile to note that the contents of CuZn -SOD-I in the serum of patients with pulmonary carcinoma were estimated to be much significantly higher than those of patients with benign pulmonary disease （P＜0.001）. The above-mentioned results indicated that in the serum of malignant tumor patients CuZn-SOD-I existed definitely.