An assay was developed using electrospray ionization negative ion tandem mass spectrometry (MS) to identify and quantitate the major product in the reaction of leukotriene A(4) (LTA(4)) with deoxyguanosine (dGuo). A second quantitative assay was established using the same separation and detection techniques to determine the amount of dGuo isolated from enzymatically processed DNA. The amount of LTA(4)-dGuo adduct could then be analytically determined in DNA samples and normalized to the amount of dGuo that had been simultaneously derived from the DNA sample. Stable isotope-labeled internal standards used for these quantitative assays were readily synthesized from isotopically labeled [(15)N(5)(13)C(10)]deoxyguanosine triphosphate and analyzed for isotopic purity using MS. A comparison of fragment ions formed from stable isotope analogs of dGuo revealed the loss of deoxyribose and secondarily the loss of a series of stable neutral small molecules in a fashion similar to patterns described previously for the collisional fragmentation of protonated guanine determined by positive ion fast atom bombardment/MS/MS. The combined quantitative assays were used for the determination of the amount of endogenously formed LTA(4)-dGuo adducts observed in DNA when isolated human neutrophils that had been incubated with arachidonic acid were stimulated with calcium ionophore to initiate leukotriene biosynthesis.