Hydrolysates of DNA that had been isolated from mouse skin treated with 3H-labelled 7,12-dimethylbenz[a]anthracene (DMBA) were subjected to chromatography on Sephadex LH20 columns and 3H-labelled products that eluted in the region expected for nucleoside-hydrocarbon adducts were purified further by high pressure liquid chromatography (h.p.l.c.). The fluorescence spectra of three major products that were resolved by this method were determined using photoncounting spectrophotofluorimetry. The fluorescence spectra of all three products were anthracene-like and similar to the spectra of nucleoside-hydrocarbon adducts obtained from DNA that was incubated with 3,4-dihydro-3,4-dihydroxy-7,12-dimethylbenz[a]anthracene 1,2-oxide (DMBA-3,4-diol 1,2-oxide). This is consistent with the idea that the metabolic activation of DMBA in mouse skin occurs through the formation of 'bayregion' diol-epoxides in the 1,2,3,4-ring.