This is a surgical lobectomy specimen of small cell lung carcinoma (SCLC) combined with large cell neuroendocrine carcinoma exhibiting extensive tumor involvement of bronchial epipthelium, glands and glandular ducts. Much of the mucosal involvement is not immediately adjacent to areas of invasive SCLC. Although it has been suggested (and it is possible) that mucosal tumor involvement in this case represents invasion by underlying invasive tumor, I believe that that explanation is unlikely. A precursor of SCLC has not yet been identified. Its identification and acceptance would require studies carefully focusing on the examination of the bronchial mucosa in a large number of resection and/or autopsy specimens. At the present time present specimens of this type are not often encountered in any one institution.