We have used a combination of thin-layer chromatography (TLC) and high pressure liquid chromatography (HPLC) to achieve separation of 32P-postlabelled 7-methylguanine and 7-(2-hydroxyethyl)-guanine adducts. The level of these two adducts was determined in human total white blood cells (mean values 0.7 to 1.5 adducts per 10(7) normal nucleotides) and isolated lymphocytes (mean values 1.1 to 12 adducts per 10(7) normal nucleotides). The separation of these two adducts revealed that the level of 7-(2-hydroxyethyl)-guanine was twice the level of 7-methylguanine adducts in total white blood cells, whereas, in isolated lymphocytes it was at least four times more than the 7-methylguanine adduct. The combined level of these two adducts in the lymphocytes of non-smokers was 1.1 to 8.4 adducts per 10(7) normal nucleotides and in the lymphocytes of smokers, the level was 5.6 to 12 adducts per 10(7) normal nucleotides. We also report detection of three unidentified adducts in the samples analysed, and at least one of these adducts seemed to be related to smoking. The chromatographic behaviour and depurination at neutral pH indicated the probable 7-alkylguanine or 3-alkyladenine nature of these unidentified adducts.