Mouse monoclonal antibody MON-114 was generated upon immunization with a human small cell lung carcinoma cell line GLC-19. Immunohistochemical analysis of normal tissues with MON-114 showed staining of the adrenal gland, brain and peripheral nerves. With respect to human lung carcinomas, 7 out of 8 small cell lung carcinomas were positively stained as well as 5 out of 5 carcinoid tumors, whereas only 4 out of 31 squamous cell carcinomas and 3 out of 19 adenocarcinomas were weakly stained. Furthermore, 1 large cell carcinoma was negative for MON-114 staining. Apparently, MON-114 stains cells of neuroendocrine differentiation.