The aim is to investigate the effects of tumornecrosis factor ?(TNF?0 and interferon a(IFN?) on the cytotoxicity of mitomycin C(MMC) in vitro. The cytotoxicity of the three agents against gastric cancer cell line and freshly isolated gastric cancer cells were determined by the MTT assay. TNF? and/or IFN? (each 0~5000U/ml) showed cytotoxicity effects only on one of ten cell cultures dose-dependently; the combination resulted in a more significant effect. The combination of MMC with TNF? (30U/ml) or IFN?(l00U/ml) could enhance the cytotoxicity of MMC on two of three cell cultures synergisticly. When three agents were used together, the cytotoxicity of MMC against the ten cell cultures was enhanced synergisticly. TNF? and IFN? could enhance the cytotoxicity of MMC synergisticly, and this may make the cancer chemotherapy more effective.