The aim of the present study was to investigate the expression of nm23-H1 in human placenta, hydatidiform mole and choriocarcinoma cells. Nm23-H1 protein was localized in the cytotrophoblast, but not in the syncytiotrophoblast. In the hydatidiform mole cases with subsequent spontaneous remission, nm23-H1 mRNA levels were significantly lower than those in first-trimester placentas. However, its levels were elevated in the hydatidiform mole cases that progressed to persistent gestational trophoblastic disease and were comparable to those of first-trimester placentas, and they were further elevated in choriocarcinoma cells. The present data suggest an association of nm23-H1 for the proliferation activity of trophoblast, and its increased expression may influence the development of persistent trophoblastic disease.