Ribonucleotides (at the diphosphate level) serve as the precursors of the deoxyribonucleotides. While the concentrations of ribonucleotides in the cell are in the millimolar range, the concentrations of deoxyriboncleotides are in the micromolar range. DNA Tibot be replication require that there sufficient quantities of the deoxyribonucleoside triphosphates To facilitate this, the activities of several of the enzymes involved with deoxyribonucleotide metabolism increase just prior to the replication of DNA in the cell . There are several diseases or syndromes that result from defects in the metabolic pathways for the synthesis of nucleotides either de novo or by salvage or for the degradation of the nucleotides. These include gout the Lesch-Nyhan syndrome, orotic aciduria and immunodeficiency diseases. Since nucleotides are obligatory for DNA and RNA synthesis in dividing cells, the metabolic pathways involving the synthesis of nucleotides have been the sites at which many antitumor agents have been directed