The reactivity of 74 lung-derived monoclonal antibodies (MAbs) provided by the Third International Workshop on Lung Tumor Antigens and of 41 non-lung-derived commercially available MAbs against sections of 15 lung tumors of various histologic types was investigated by immunohistochemistry. Three MAbs with specificity for human neural-cell adhesion molecule (H-NCAM) and 3 MAbs with specificity for small-cell lung carcinoma (SCLC) were able to distinguish between neuroendocrine (NE) and non-NE tumors. Fifteen MAbs stained non-small-cell carcinomas (NSCLC) but not SCLC. Neuron-specific enolase (NSE) stained all NE tumors but also some of the non-NE tumors. Two MAbs showed specificity for mesotheliomas. Carcino-embryonic MAb strongly stained all SCLC and NSCLC. Among MAbs with lymphoid-cell specificities, Leu 7 (CD57) stained SCLC, but not NSCLC. LN2 (CD45R), LN3 (HLA-DR), Leu 22 (CD43) and BLA 36 reacted with NSCLC and were non-reactive with SCLC. Some of the lung-derived MAbs showed immune staining of lymphoma and melanoma.