The in vitro adduct formation between phenyl glycidyl ether (PGE) and calf thymus DNA was investigated. Agarose slab gel electrophoresis of DNA incubated with PGE revealed that nearly all high-molecular-weight species were degraded after 10 h of incubation. After DNA precipitation the reaction products present in the supernatant were subjected to a solid-phase extraction on a polystyrene divinylbenzene copolymer, enabling analysis on capillary zone electrophoresis (CZE), using sample stacking. These reaction products were mainly produced during the first 10 h of incubation, indicating that these products result from the DNA degradation. On the other hand, analysis of the adducts present in the enzymatic digest of the DNA pellet revealed that these adducts were formed only after 10 h of incubation. The reaction products present in the DNA supernatant were identified by on-line coupling of CZE to electrospray tandem mass spectrometry. Three major reaction products resulted from phosphate alkylation, as proven by the analysis of the corresponding low-energy CAD product ion mass spectra. This phosphate alkylation results in phosphotriesters which readily hydrolyze, resulting in DNA strand breaks.