Objective: The nm23 gene has been identified as a potential metastasis suppressor gene in various human neoplasms. Both Bcl-2, which promotes cell survival, and Bax, which promotes cell death, have been considered as major factors in controlling the apoptotic pathway. This study was carried out to determine whether these markers are useful in distinguishing potential intrinsic differences in tumor virulence of papillary thyroid cancers. Material and Method: The expressions of nm23, Bcl-2 and Bax have been evaluated using immunohistochemical techniques in 100 pure papillary thyroid cancers and 20 metastatic lymphnodes. The intensity of immnunoreactivity was graded on arbitrary four point scale(grade 0 or 1 : negative reactivity, grade 2 or 3 positive reactivity). The immunoreactivities were analyzed in relation to TNM atage, AMES score, local recurrence and distant metastasis, and that of metastatic LNs was compared with the tumors. Results: The expression of Bcl-2 and bax did not show any statistical differences by TNM stage, AMES score, recurrence, distant metastasis and also between the tumor and metastatic LN. However, the nm23 showed higher expression of Ki67 in distant metastasis than in control group and in metastatic LNs than in the tumors(p<0.05). Conclusion: Although the expression of Bcl-2 and Bax protein showed no correlation with clinical parameters representing tumor virulence, the nm23 expression could be an useful prognostic factor, especially in predicting nodal or distant metastasis in papillary thyroid cancer.