To examine the possibility of cytokine gene therapy in relation to pancreatic cancer, we evaluated the antitumor effect of human pancreatic carcinoma cells (AsPC-1) which were retrovirally-transduced with several kinds of cytokine genes. These cells were inoculated into BALB/c nude mice and their tumor volumes were assessed. The in vitro growth rate of the transduced cells was not different from that of a parental cell line. Among the transduced cells, human interleukin (IL)-6-transduced AsPC-1 and mouse granulocyte macrophage colony-stimulating factor-transduced AsPC-1 cells showed a significant retardation of tumor growth compared with a parental cell line. In the cases of AsPC-1 cells transduced with the human IL-2 or mouse IL-4 gene, small tumors were generated but thereafter they regressed completely. Histological examinations showed monocytic cell infiltration around the tumors of IL-2- or IL-4-producing cells. These data suggest that secretion of IL-2 or IL-4 from tumor cells can induce an antitumor effect even in the defective condition of mature T cells.