In the first part of the chapter, emphasis is placed on the description of the main reactions of radical cations of the four predominant DNA purine and pyrimidine bases and minor 5-methylcytosine in aerated aqueous solutions. Information is also provided on the final one-electron oxidation products of 8-oxo-7,8-dihydroguanine, an ubiquitous decomposition product of DNA with most chemical and physical oxidizing agents, that exhibits a low ionization potential, and is therefore an excellent sink for positive hole migration within double-stranded DNA. In the second part of the review, it is shown that duplex stability plays a major role in the redistribution of positive holes generated by high intensity UV laser pulses on purine and pyrimidine bases towards guanine residues. These results were obtained by measurement of several oxidized nucleosides within DNA using a sensitive and accurate high performance liquid chromatography-tandem mass spectrometry assay.