Two hair dye components, carcinogenic 4-nitro-2-aminophenol and 5-nitro-2-aminophenol, induced Cu(II)-dependent DNA cleavage frequently at thymine and guanine residues in DNA fragments obtained from the c-Ha-ras-1 protooncogene. When the p53 tumor suppressor gene was used, 4-nitro-2-aminophenol caused Cu(II)-dependent piperidine-labile sites at poly G sequences. In the presence of Cu(II), both components increased 8-oxo-7,8-dihydro-2'-deoxyguanosine formation in DNA. The inhibitory effects of catalase and bathocuproine on DNA damage suggest the involvement of H2O2 and Cu(I). It is speculated that nitro-2-aminophenols undergo Cu(II)-mediated autoxidation to generate active oxygen species causing DNA damage which leads to their carcinogenesis.