The possibility to induce the formation of covalent cross-links between polyamines and guanine following one electron oxidation of double stranded DNA has been evaluated. For such a purpose, a strategy has been developed to chemically synthesize the polyamine-C8-guanine adducts, and efforts have been made to characterize them. Then, an analytical method, based on HPLC separation coupled through electrospray ionization to tandem mass spectrometry, has been setup for their detection and quantification. Using such a sensitive approach, we have demonstrated that polyamine-C8-guanine adducts could be produced with significant yields in double stranded DNA following a one-electron oxidation reaction induced by photosensitization. These adducts, involving either putrescine, spermine, or spermidine, are generated by the nucleophilic addition of primary amino groups of polyamines onto the C8 position of the guanine radical cation. Our data demonstrate that such a nucleophilic addition of polyamines is much more efficient than the addition of a water molecule that leads to 8-oxo-7,8-dihydroguanine formation.