The primary neuroendocrine carcinomas[NEC] of the lung are relatively rare. There are classified histologically into the following groups. 1] bronchial carcinoid, 2] well differentiated neuroendocrine carcinoma[WDNC], 3] intermediate cell neuroendocrine carci-noma[ICNC], 4] small cell neuroendocrie carcinoma[SCNC]. The NE cells can be found throughout the mucosa of the bronchial tree by the electron microscopy. By the immunocytochemistry, Neuron-specific enolase[NSE], serotonin, born-csin, and calcitonin are found in normal solitary NE cells and neuroepithelial bodies. The immunohistochemistry has the advantage that it can be applied on routine pathology specimens. The NSE was localized in all of the NE granule bearing tumors but also present in 57 per cent of the non NE carcinomas. Together the combination of chromogranin A, bombesin and NSE should provide an exellent signature for tumor cells expressing NE features, such as carcinoids and other NE carcinomas. We have experienced two cases of primary pulmonary NEC in 59 and 29 years old men. The former was admitted due to exertional dyspnea and left chest pain, the latter, newly developed mass on chest X-ray. They were treated by Lt pneumonectomy with LN dissection and RLL resection with LN dissection The postoperative diagnoses were could be confirmed by NSE study as NEC which were SCNEC and INEC in subgroups. The postoperative courses were uneventful.