When a synthesized deoxyribonucleotide duplex, 5'-CCATCG*CTACC-3'center dot 5'-GGTAGCGATGG-3', containing a trans 14R dibenzo[a,l] pyrene (DB[a,l]P) adduct, corresponding to trans opening of the (+)-(11S, 12R)-diol (13R,14S)-epoxide by N-2 of the central G* residue, was allowed to stand for 2-6 days at ambient temperature in neutral aqueous solution, three new products were observed on denaturing HPLC. One of these corresponded to loss of the DB[ a, l] P moiety from the original adducted strand to give an 11-mer with an unmodified central dG. The other two products resulted from a highly unexpected migration of the hydrocarbon moiety to either dG(5) or dG(7) of the complementary strand, 5'-GGTAG(5)CG(7)ATGG-3'. Enzymatic hydrolysis of the two 11-mer migration products followed by CD spectroscopy of the isolated adducted nucleosides indicated that, in both cases, the hydrocarbon moiety had undergone configurational inversion at C14 to give the cis 14 S DB[a,l]P dG adduct. MS/MS and partial enzymatic hydrolysis showed that the major 11-mer had the hydrocarbon at dG(7). Two 11-mer oligonucleotides were synthesized with a single cis 14S DB[a,l]P dG adduct either at G(7) or at G(5) and were found to be chromatographically identical to the major and minor migration products, respectively. Although HPLC evidence suggested that a small extent of hydrocarbon migration from the trans 14 S DB[ a, l] P dG diastereomer also occurred, the very small amount of presumed migration products from this isomer precluded their detailed characterization. This interstrand migration appears unique to DB[a,l]P adducts and has not been observed for their fjord-region benzo[c] phenanthrene or bay-region benzo[a]pyrene analogues.