Peripheral blood monocytes from 15 cases of malignant bone tumors and 12 cases of health volunteers were seperated and induced by lipopolysaccharide(LPS) for 48-hour culture. The supernatant was collected for determining the content of nitrite and tumor necrosis factor-alpha(TNF-alpha) (by Griess and ELISA methods, respectively). The results were as follows: The content of nitrite and TNF-alpha in patients with malignant bone tumors was significantly higher than that in normal control; the content of nitrite and TNF-alpha in the malignant bone tumor group presented the positive correlation (r = 0.8909, P < 0.01). The results suggest that NO and TNF-alpha produced by activated macrophages may be related to the pathogenesis of malignant bone tumors.