To compare the anti-tumor effects of transmembrane TNF-alpha (TM-TNF) and secreted TNF-alpha (S-TNF) in vivo, mouse fibroblasts NIH3T3 were transfected separately with three types of retrovirus containing wild type TNF-alpha (Wt-TNF), TM-TNF mutant (TM-TNFm), S-TNF mutant (S-TNFm). Southern blot, RT-PCR, FACS and bioassay were used to investigate TNF-alpha gene integration, expression and its biological activity. It was found that both fixed cells and supernatant of NIH3T3/Wt-TNF, the fixed cells of NIH3T3/TM-TNFm and the supernatant of NIH3T3/S-TNFm could express high level of TNF-alpha or its mutants and effectively kill H22 in vitro. The transfected NIH3T3 were separately injected into the mice at the sites of H22 tumor cell inoculation according to a ratio of 5:1 or 1:1 (effector/target cells, E/T) after the third day of H22 challenge, respectively. At the E/T = 5:1, the NIH3T3/TM-TNFm induced the highest tumor regression, while NIH3T3/S-TNFm exerted the strongest tumor depressing effect at the E/T = 1:1 in vivo. No obvious side effects were noted throughout the course of treatment. The results suggest that both TM-TNF and S-TNF could cause tumor regression. The anti-tumor effect of TM-TNF would be more powerful and safe than that of S-TNF at the proper E/T ratio.