Three rat monoclonal antibodies were selected for the immunodetection of small cell lung cancer metastases in bone marrow and other hematologic samples. By membrane immunofluorescence, they define three distinct surface antigens here termed lung cancer-associated antigens or LCAs. The latter are widely expressed on small cell lung cancer and non-small cell lung cancer cells/cell lines, but not detectable on a variety of normal and transformed bone marrow, blood and lymphoid cells. Anti-LCA1 (IgM) is similar to the many anti-lacto-N-fucopentaose III IgM antibodies rasied against human tumors. In contrast, anti-LCA2 (IgG2b) and anti-LCA3 (IgG2a) define surface proteins of 29, 32, 41 and 98 kilodaltons, respectively, that have not been reported earlier. These three reagents have immunodiagnostic potential, since in combination they label all 49 lung cancer cell lines tested. Their ability to detect lung cancer metastases in patient's bone marrow samples is documented in an accompanying paper.