Cytotoxic nucleoside analogs (NA) are important in the treatment of hematologic malignancies. The NA in routine clinical use include the pyrimidine analog cytosine arabinoside (ara-c), which is extensively used in the treatment of acute leukemias, and the purine analogs, cladribine and fludarabine. These drugs have mostly been used in the treatment of low grade hematological malignancies. NA become therapeutically effective only after phosporylation to the triphosphate level. The 5'-nucleotidases (5'-NTs) dephosphorylate the monophosphate form of NA and, therefore, may affect the pharmacological activity of these antimetabolites in the clinic. Several 5'-NTs attached to membranes or present in the cytosol or in mitochondria are present in mammalian cells. cN-II, an IMP-selective 5'-NT, participates in the regulation of purine deoxyribonucleotide metabolism. cN-II opposes the action of the salvage enzymes by dephosphorylating purine nucleoside mononphosphates to purine nucleosides. Due to its phosphotransferase activity, cN-II can also phosphorylate inosine and 2',3'-dideoxyribonucleosides utilizing IMP as a phosphate donor. The observation that cytosolic cN-II is able to phosphorylate purine nucleosides has initiated studies on its potential participation in the metabolism of anticancer agents and in the development of cN-II inhibitory substances. In this review, we highlight the current knowledge concerning cN-II activity and regulation of intracellular deoxyribonucleotide pools and it role in hematological malignancies.