Immunohistochemical reactivities of six lung cancer-associated monoclonal antibodies to the tissue sections of lung cancer, other neoplasms and normal tissues and to the Saccomanno's treated cells were analyzed using an indirect immunoperoxidase technique. The antibodies included LA-4 raised against a lung adenocarcinoma, LSO-4 and -5 against an oat cell lung cancer, LSI-a and -2 against intermediate small cell lung cancers and LE-3 against an epidermoid lung cancer. Six fixation methods were compared, and PFA fixation revealed not to change the antigenisity detected by the antibodies. LSO-4 and -5 antigens were completely dissappered by paraffin-embeded and Saccomanno's treatment. LA-4, LSI-a and -2 were reacted with normal bronchioles and lung cancer tissues. These normal differentiation antigens were expressed on the tissues of lung adenocarcinoma and small cell and epidermoid lung cancers. LE-3 antibody reacted with normal platlets and large intestine tissues, and the LE-3-reacted antigen expressed not only on lung epidermoid cancer but on lung adenocarcinoma. LE-3 did not react with normal lung tissues or Saccomanno's treated normal cells, but reacted the Saccomanno's treated epidermoid lung cancer cells, thus appered to be useful for sputum cytology.