Both the antigen presenting ability and the cytotoxicity of macrophages can be enhanced by GM-CSF gene transfer. In the present study, the therapeutic effect of intratumoral injection with GM-CSF gene.modified allogenic macrophages on tumor-beating mice observed. The peritoneal macrophages of C57BL/6 mice were transfected with GM-CSF gene mediated by recombinant adenovirus and the subcutaneous CT26 colon adenocarcinoma- bearing BALB/c mice were treated by intratumoral injection of the above macrophages. The survival time of the tumor-bearing mice were prolonged significantly and some tumor mass disappeared completely. The necroses of the tumor cells and massive infiltration of inflammatory cells were observed 6 days after treatment. 30 days after treatment, only the leftover of tumor cells and the inflammatory cells remained. The data indicated that introtumoral injection of GM-CSF gene-modified allogenic macrophages displayed more potent therapeutic effect on the preestablished tumor-bearing mice.