It was proposed that nm23 gene may function as a suppressor gene for tumor metastasis. Using an antibody to NDPK, levels of NDPK/nm23 expression in lung carcinomas were examined immunohistochemically, 45 of 58 squamous carcinomas and 26 of 36 adenocarcinomas showed strong immunoreactivity for NDPK/nm23 in most of cancer cells within tumor tissues. On some normal bronchial epithelium and serous glands, there also show weak expression. No relationship was found between NDPK/nm23 expression and clinicopathological parameters including tumor grade, size, nodal involvement and stage but the increases in NDPK/nm23 expression were stronger in advanced stages of squamous cell carcinomas. In conclusion, our results indicate that the increased NDPK/nm23 expression in the analysed carcinomas is not consistent with the proposed metastasis-suppressor function, but the nm23 gene may be implicated in the mechanism of carcinogenic process and tumor progression.