This scheme is based on the results from DNA adduct detection in lung and bladder tissues of mice exposed to MST and SSS, DNA adduct analysis in lung tissues of tobacco smokers versus non-smokers, and results of analysis of aldehyde effect on DNA adduct induction, DNA repair activity, repair protein levels, and mutagenesis susceptibility in cultured human lung and bladder epithelial cells (19, 20, 61). Symbols: NNK, nicotine- derived nitrosamine ketone; NNN, N-nitrosonornicotine; AhR, aromatic hydrocarbon receptor; AAs, aromatic amines; CYPs, cytochrome p450s; NAs, nitrosamines; Acr, acrolein; Cro, crotonaldehyde; Fal, formaldehyde; LPO, lipid peroxidation; PBDs, pyridylic-butylic derivatives; PAHs, polycyclic aromatic hydrocarbons; PAHDEs, PAH diol epoxides.