Benzo(a)pyrene (BaP) is highly carcinogenic in rats but is without effect in rabbits when administered s.c. The possibility that BaP-DNA adducts could be responsible for this species difference was investigated by comparing BaP-deoxyribonucleoside adducts formed in dermal fibroblast cultures from Wistar rats and New Zealand rabbits. Treatment with [G-3H]BaP (1.2 microM) for 6, 24, and 48 h produced an essentially qualitative species-specific difference. Over 95% of the DNA adducts in the rabbit dermal cell cultures were derived from anti-BaPDE; the major BaP adduct formed (90%) was (+)-anti-BaPDE-deoxyguanosine. This adduct was formed at very low levels in the rat dermal fibroblasts (7%). These cells contained a large proportion of (+/-)-r-7,t-8-dihydroxy-c-9,10-oxy-7,8,9,10-tetrahydrobenzo(a)pyrene (syn-BaPDE)-DNA adducts (45%) and over 48% of other, unidentified, BaP-DNA adducts. Cells treated with (-)-BaP-7,8-diol (1.2 microM) produced almost exclusively (greater than 99%) (+)-anti-BaPDE-deoxyguanosine in rabbit cells, while the rat cells did not form this product. These results suggest that adducts other than anti-BaPDE-deoxyguanosine may be involved in rat s.c. BaP carcinogenesis; the preferential formation of (+)-anti-BaPDE-deoxyguanosine by rabbit dermal fibroblasts does not directly correlate with the resistance of rabbit dermis to tumor formation.