High performance liquid chromatography (HPLC)/electrospray mass spectrometry methods were developed for the analysis of 1,N2-etheno(epsilon)guanine (Gua) and 5,6,7,9-tetrahydro-7-hydroxy-9-oxoidmidazo[1,2-a]purine (HO-ethanoGua) [the cyclized form of N2-(2-oxoethyl)Gua] and its deoxyribose derivative in DNA. Evidence was provided for the formation of the latter adduct in DNA treated with 2-chlorooxirane, the reactive product formed from the carcinogen vinyl chloride. Measured levels of HO-ethanoGua and HO-ethanodeoxyguanosine were similar, although the assay for the deoxyribosyl derivative has some technical advantages. 3,N4-epsilon-Deoxycytidine was also estimated in 2-chlorooxirane-treated DNA using HPLC with fluorescence detection. Levels of all known adducts formed from vinyl chloride have now been estimated in DNA treated with 2-chlorooxirane and vary in the order N7-(2-oxoethyl)Gua > 1,N6-epsilon-adenine > HO-ethanoGua > N2,3-epsilon-Gua > 3,N4-epsilon-cytosine > 1,N2-epsilon-Gua. Although in vivo adduct levels may not parallel these due to differential stability and rates of repair, analyses of the adducts in DNA treated with 2-chlorooxirane provide a basis for consideration of the biological effects of these adducts.