BACKGROUND: Transforming growth factor- alpha(TGF-alpha) may play important roles in carcinogenesis, tumor growth, and angiogenesis. Transforming growth factor-beta(TGF-beta) 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-beta. METHOD: To evaluate the possible role of TGF-alpha and TGF-beta in human primary lung cancers, the expression of TGF-alpha and TGF-beta 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-beta 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-beta was discernible in bronchial epithelium in eight of ten non-cancerous lung tissues. The expression of TGF-beta was noted in the cytoplasms of tumor cells in eight cases of forty seven(17.0%) primary lung cancers. The expression of TGF-beta 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-beta are involved during development and growth of primary lung cancers.