It has been shown that IL-2 and IL-6 can cooperate to induce immune responses more effectively. In order to increase the therapeutic efficacy of cytokine gene-transfected tumor vaccines, we treated the experimental pulmonary metastatic melanoma-bearing mice with IL-2 gene-transfected tumor vaccine and IL-6 gene-transfected tumor vaccine. After the combined treatment, the pulmonary metastases were reduced more significantly and the survival time of tumor-bearing mice was also prolonged more significantly. The CTL activity, NK activity and IL-2-induced LAK activity, IL-2 and TNF secretion from the splenocytes of the above tumor-bearing mice increased more significantly than that of tumor-bearing mice treated with IL-2 gene-transfected vaccine or IL-6 gene-transfected vaccine alone. These results demonstrated that the combined use of IL-2 gene-transfected tumor vaccine and IL-6 gene-transfected tumor vaccine could achieve more potent antitumor effect via more efficient activation of immune functions. The experiment outlines a novel approach to the cytokine gene therapy of cancer.