The family of Nm23/NDPK (nucleoside diphosphate kinase) proteins regulates a vast variety of cellular processes and, therefore, participates in important physiological events like proliferation, differentiation, molecular transport, and apoptosis. The majority of experimental data concerning this gene family has been focused on their engagement in metastasis formation--a critical point in tumor progression. In spite of the growing amount of evidence suggesting the multifunctional role of nm23/NDPKs the specific functions of every particular family member is still elusive. This review focuses on recent evidence on specific subcellular localization of Nm23-H1/NDPK A and Nm23-H2/NDPK B proteins and attempts to connect the findings to their diverse biological functions in the normal and/or malignantly transformed cell.