A procedure is described for the preparation of 2'-deoxy-4-pyrimidinone (dH2U) and 2'-deoxy-5-methyl-4-pyrimidinone (dH2T) nucleosides. The key transformation is a nearly quantitative desulfurization of the corresponding 2-thio analogue by a brief treatment with a m-chloroperbenzoic acid/pyridine solution. The phosphoramidites of these nucleosides have also been synthesized.