The expression of p⁵³ protein, c-erbB-2 oncoprotein, proliferating cell nuclear antigen (PCNA) were studied by the streptavidin peroxidase conjugated (S-P) immunohistochemical method and DNA content in situ was tested, in order to explore the significance of p⁵³, c-erbB-2, PCNA in primary lung carcinoma.