Bifunctional　alkylating　agent　1,3-Bis-(2-chloroethyl)-1nitrosourea　(BCNU)　is　a　significant　anticancer　drug　in　the　clinical　treatment　of　human　malignancies.　A　serious　complication　of　treatment　with　BCNU　is　the　increased　risk　of　a　secondary　leukaemia　in　long-term　survivors　because　not　all　alkylating　agent　interactions　with　DNA　result　in　cell　death.　In　the　present　work,　high-performance　liquid　chromatography　(HPLC)　was　combined　with　electrospray　ionization　tandem　mass　spectrometry　(ESIMS/　MS)　to　develop　a　sensitive　and　selective　method　for　the　measurement　of　DNA　adducts　induced　by　BCNU.　Double　strand　calf　thymus　DNA　was　treated　with　BCNU　and　digested　enzymatically　down　to　the　nucleoside　level.　The　hydrolysates　were　analyzed　by　HPLC　separation　followed　by　electrospray　ionization　tandem　mass　spectrometry.　The　main　alkylated　products,　N-7-(2-hydroxyethyl)　deoxyguanosine　(N-7-HOEtdG),　N-7-(2-chloroethyl)　deoxyguanosine　(N-7-ClEtdG)　and　1-[　N(3-)deoxycytidyl]-2-[　N-1-deoxyguanosyl]　ethane　(dG-dC)　were　qualitatively　detected　and　quantitatively　characterized　by　selected　reaction　monitoring　(SRM)　mode.