The effectiveness of noninfectious recombinant adenovirus encoding murine granulocyte-macrophage colony stimulating factor (mGM-CSF) for the treatment of Meth A fibrosarcoma was investigated in syngeneic BALB/C model. Meth A and HeLa cells transduced with the recombinant adenovirus (Ad.mGM-CSF) produced substantial amounts of mGM-CSF, while WEH1164 cells transduced with the virus did not produce mGM-CSF. Mice inoculated subcutaneously with $1{ imes}10^6$ Meth A cells, followed by injection of Ad.dE1 as a control, developed large tumors that reached a mean tumor size of 22 mm by day 30. However, tumor development and tumorigenicity were significantly inhibited in mice with a single intratumoral injection of Ad.mGM-CSF at $1{ imes}10^8;pfu$. Histological examination of the tumors injected with Ad.mGM-CSF revealed dense infiltrates of neutrophils, histiocytes, lymphocytes, and eosinophils associated with apoptotic cell death. The results suggest that the recombinant adenovirus encoding GM-CSF have a potential use for cancer gene therapy.