A simple and convenient method has been developed for the synthesis of a N7-guanine adduct of sulfur mustard (SM), which can serve as an efficient biomarker for alleged exposure to SM. The adduct obtained in high yields (~78%) was characterized on the basis of its physical properties and spectral data. In addition, HPLC and LC-MS conditions have been standardized for the detection of the adduct in both in vitro and in vivo samples, which is useful for retrospective detection of exposure to SM in biological samples.Key words: sulfur mustard, biomarker, N7-guanine adduct, in vitro, in vivo, HPLC, LC-MS, electrospray, 2D NMR.