Background: Transforming growth factor- alpha(TGF-$alpha$) may play important roles in carcinogenesis, tumor growth, and angiogenesis. Transforming growth factor-beta(TGF-$eta$) are known to be involved in cell-cycle control and regeneration. TGF-$alpha$ positively acts on growth control of many epithelial cells in contrast to the negative role of TGF-$eta$. Method: To evaluate the possible role of TGF-$alpha$ and TGF-$eta$ in human primary lung cancers, the expression of TGF-$alpha$ and TGF-$eta$ were immmunohistochemically investigated in tissue sections from forty seven cases with lung cancers and ten cases with non-cancerous lung tissues. Recombinant cloned monoclonal antibody of TGF-$alpha$ and neutralizing antibody of TGF-$eta$ were employed as primary antibodies after dewaxing the formalin-fixed, paraffinized tissue sections. Results: TGF-$alpha$ was expressed in the cytoplasms of tumor cells in thirty five cases of forty seven(74.5%) primary lung cancers, whereas the control expressed in two of ten brochial epithelial cells. The expression of TGF-$alpha$ was disclosed in four cases of eleven(36.4 %) small cell carcinomas and thirty one cases of thirty six(86.1%) non-small cell carcinomas of the lung. Expressions of TGF-$eta$ was discernible in bronchial epithelium in eight of ten non-cancerous lung tissues. The expression of TGF-$eta$ was noted in the cytoplasms of tumor cells in eight cases of forty seven(17.0%) primary lung cancers. The expression of TGF-$eta$ disclosed in two cases of eleven(18.2%) small cell carcinomas and six cases of thirty six(16.7%) non- small cell carcinomas of the lung. Conclusion: These findings suggest that up-regulation of TGF-$alpha$ and down-regulation of TGF-$eta$ are involved during development and growth of primary lung cancers.