The two major metabolic pathways of benzo[a]pyrene (BP), as well as other polycyclic aromatic hydrocarbons, that allow for the induction of DNA lesions are monooxygenation that results in diol epoxides (BPDE), and one-electron oxidation that yields a BP radical cation. The DNA adducts formed at the -NH2 group of Gua and Ade via the monooxygenation pathway are stable, while those formed at the skeletal nucleophilic centers of Gua and Ade by the radical cation pathway are unstable, i.e. they undergo depurination. Mutations resulting from both stable and depurinating DNA-BP adducts have been argued to be important in carcinogenesis. Most in vivo animal studies with BP, however, have employed dosage/DNA adduct levels several orders of magnitude higher than those expected from environmentally relevant exposures that have been estimated to result in a damage level of ~1 adduct/107 bp of DNA. Presented are results of experiments in which A/J strain mice were exposed to BP (single intraperitoneal (i.p.) injection, 50 ?g/g dose) which establish that non-line narrowed fluorescence and fluorescence line narrowing spectroscopies possess the selectivity and sensitivity to distinguish between helix external, base-stacked, and intercalated conformations of DNA-BPDE adducts formed in lung tissue. Concentrations measured by 32P-postlabeling two and three days after i.p. injection were 420-430 and 600-830 amol BPDE-type adducts per ?g DNA. The external and base-stacked conformations are attributed mainly to (+)-trans-anti-BPDE-N2dG and the intercalated conformations to (+)-cis-anti adducts. A stable adduct derived from 9-OH-BP-4,5-epoxide was also detected at a concentration about a factor of 10 lower than the above concentrations. A depurinating adduct, BP-6-N7Gua, was identified in the lung DNA extraction wash of one of the mice studied by CE-laser induced fluorescence and HPLC-MS at a concentration of ~2.5 fmol per ?g of DNA. The results are discussed in terms of earlier in vitro and in vivo studies of stable and depurinating DNA adducts formed from BP.