Expression of nucleoside diphosphate(NDP) kinase, which is homologous to the nm23 gene product in a variety of species, has been found to be inversely associated with metastatic potential. However, the relationship remains controversial according to the tumor cell types and experimental system, with conflicting results from different research groups. In order to determine whether NDP kinase expression serves as a marker for metastatic potential in human skin cancer, we assessed the levels of NDP kinase expression in 9 keratoacanthomas (KAs), 26 squamous cell carcinomas (SCCs), and 25 basal cell carcinomas (BCCs) using immunohistochemistry. The expression of NDP kinase was intense in KA and SCC compared with BCC. However, the difference of NDP kinase expression between KA and SCC was not statistically significant. And there was no statistically significant difference in NDP kinase expression between SCC with metastasis and SCC without metastasis. Our results contradict the hypothesis concerning the possible role of nm23 gene as a metastatic suppressor gene in human skin cancer. The mechanism of overexpression in various tumor cell types and its biological significance in cutaneous carcinogenesis remain to be determined.