Formation of DNA adducts, following treatment of primary rabbit tracheal epithelial cells (RTEC) with 1,8-dinitropyrene (1,8-DNP) and its partially reduced derivative, 1-nitro-8-nitrosopyrene (1,8-NONO2), was examined using the 32P-post-labelling technique. Treatment of aerobic cells with 1,8-DNP or 1,8-NONO2 produced qualitatively similar results. Cochromatography showed that the major adduct observed corresponded to the major adduct seen following treatment of poly(dG.dC) with N-hydroxyl-1-amino-8-nitropyrene, generated from 1,8-NONO2. A minor adduct migrated to the same area on the TLC plate as the major compound observed following a similar treatment with poly(dA.dT). Relative adduct labelling (RAL) values were consistently an order of magnitude higher with 1,8-NONO2 than with 1,8-DNP, suggesting that reduction of a nitro group of 1,8-DNP to a nitroso group may be a rate-limiting step in the cells. In studies on the formation and persistence of the 1,8-NONO2 adduct in RTEC maximum binding was observed at 1 h. Fifteen hours later the RAL value was less than 15% of this maximum level.