The murine nm23, a putative metastasis suppressor, has three human homologues, NM23-H1, -H2, and -H3b. Several reports have suggested a low metastatic potential for neoplasms with a high expression of NM23-H1 gene, while other studies have not shown this relationship. These apparent differences in the role of NM23 in metastasis suppression might be explained by unability to discriminate between the expression of the two genes NM23-H1 and NM23-H2. The NM23-H2 product is not related to tumor progression and metastasis suppression. Two studies on human oral squamous cell carcinoma (OSCC) have been reported, both showing the NM23 product to be a metastasis suppressor factor. However, none of these two studies distinguished NM23-H1 from NM23-H2. The aim of this study was to detect the protein expression pattern of NM23-H1 product in 24 OSCCs by immunohistochemistry in paraffin-embedded tissues using a monoclonal antibody non-cross-reactive with NM23-H2. The NM23-H1 positive group showed lower frequency of lymph node metastasis, and a better grading than the NM23-H1 negative group supporting the role of NM23-H1 as metastasis suppressor factor which may be useful for predicting tumor metastasis in OSCC.