Abstract: Plasmid DNA containing transforming growth factor β₁ （TGFβ₁） gene was directly injected into subcutaneous nodules of murine lung adenocarcinoma in T ₇₃₉ mice. Post injection observation showed that the growth of tumor was significantly boosted in the treated mice as compared with the control groups （pMAM_neo DNA or saline）, whereas there was no significant difference in metastatic behavior. Both Northern and slot blot confirmed efficient expression of TGFβ₁ mRNA in the treated group but not in the control. The results suggest that direct intratumoral injection of nude plasmid DNA might be a promising gene transfer strategy in vivo.