Catechol, a naturally occurring and an important industrial chemical, has been shown to have strong promotion activity and induce glandular stomach tumors in rodents. In addition, catechol is a major metabolite of carcinogenic benzene. To clarify the carcinogenic mechanism of catechol, we investigated DNA damage using human cultured cell lines and 32P-labeled DNA fragments obtained from the human p53 and p16 tumor suppressor genes and the c-Ha-ras-1 proto-oncogene. Catechol increased the amount of 8-oxo-7,8-dihydro-2'-deoxyguanosine (8-oxodG), which is known to be correlated with the incidence of cancer, in a human leukemia cell line HL-60, whereas the amount of 8-oxodG in its hydrogen peroxide (H2O2)-resistant clone HP100 was not increased. The formation of 8-oxodG in calf thymus DNA was increased by catechol in the presence of Cu(2+). Catechol caused damage to 32P-labeled DNA fragments in the presence of Cu(2+). When NADH was added, DNA damage was markedly enhanced and clearly observed at relatively low concentrations of catechol (<1 microM). DNA cleavage was enhanced by piperidine treatment, suggesting that catechol plus NADH caused not only deoxyribose phosphate backbone breakage but also base modification. Catechol plus NADH frequently modified thymine residues. Bathocuproine, a specific Cu(+) chelator and catalase inhibited the DNA damage, indicating the participation of Cu(+) and H2O2 in DNA damage. Typical hydroxyl radical scavengers did not inhibit catechol plus Cu(2+)-induced DNA damage, whereas methional completely inhibited it. These results suggest that reactive species derived from the reaction of H2O2 with Cu(+) participates in catechol-induced DNA damage. Therefore, we conclude that oxidative DNA damage by catechol through the generation of H2O2 plays an important role in the carcinogenic process of catechol and benzene.