The reaction of trans-7,8-dihydroxy-anti-9,10-epoxy-7,8,9,10-tetrahydrobenzo(a)pyrene (anti-BPDE) with DNA prelabelled with [14C] and [3H]-purine precursors has indicated that in addition to the N2-position of guanine previously reported [10--12] reaction also involves the N7-position of guanine. The hydrocarbon-N7-guanine product was not detected earlier because it is lost from the DNA very readily at pH 7. The same N7-product was obtained by reaction of anti-BPDE with guanine in dimethylformamide.