Relationships of nm23 expression and 12 clinicopathologic variables and proliferative activity of cancer cells were examined in 55 gastric cancer patients to clarify the effects of nm23 expression on the factors and activity in gastric cancer. Expression of nm23 was determined by immunohistochemically stained sections using a monoclonal antibody, nm23H-1. Proliferative activity was immunohistochemically evaluated by proliferating cell nuclear antigen (PCNA) labeling index (LI) using a monoclonal antibody PC10. Expression of nm23 was found in 24 lesions (positive group) but not in 31 lesions (negative group). With regard to clinicopathologic variables, a significant (p < 0.05) difference between the positive and negative groups was found in 1 of the 12 factors, depth of cancer invasion. PCNA LI (48.9 +/- 11.6%) of the former group was significantly (p < 0.05) higher than that (40.3 +/- 12.6%) ot the latter, although multiple regression analysis showed that nm23 expression was not one of the most influencing variables for PCNA LI. The results may suggest that expression of nm23 in gastric cancer lesions is correlated to tumor progression and/or proliferation rather than suppression of metastasis.