Capillary liquid chromatography/microelectrospray mass spectrometry has been applied to the detection of deoxyribonucleoside adducts of the food- derived mutagen 2-amino-3-methylimidazo[4,5-f]quinoline (IQ) from in vitro and in vivo sources. Constant neutral loss (CNL) and selective reaction monitoring (SRM) techniques with a triple-quadrupole mass spectrometer enabled sensitive and specific detection of IQ adducts in vitro and in animals. Detection of 1 adduct in 104 unmodified bases is achieved using CNL scanning detection, while the lower detection limits using SRM approach 1 adduct in 107 unmodified bases using 300 μg of DNA. The DNA adducts N- (deoxyguanosin-8-yl)-2-amino-3-methylimidazo[4,5-f]quinoline (dG-C8-IQ) and 5-(deoxyguanosin-N2-yl)-2-amino-3-methylimidazo[4,5-f]quinoline (dG-N2-IQ) were detected in kidney tissues of chronically treated cynomolgus monkeys at levels and in proportions consistent with previously published 32P- postlabeling data [Turesky, R. J., et al. (1996) Chem. Res. Toxicol. 9, 403- 408]. Thus, capillary tandem LC/MS is a highly sensitive technique, which can be used to screen for DNA adducts in vivo.