To evaluate the genetic toxicity of 1, 4-dichlorobenzene (p-DCB), DNA adducts of p-DCB were analyzed in in vitro and in in vivo. In the in vitro study, calf thymus DNA (400 μg/ml) was mixed with p-DCB (100 μM), liver microsome (1 mg protein/ml) and an NADPH-regenerating system. After incubation at 37°C for 1 hr, DNA was isolated and purified for DNA adduct analysis. There were no DNA adducts detected when p-DCB was metabolized by rat, mouse or human liver microsomes. In the in vivo study, Fischer 344 rats were given different kinds of cytochrome P450 (CYP) inducers and then injected with p-DCB. Twenty-four hr after injection, livers were collected from the rats for DNA adducts analysis. We did not find any p-DCB DNA adducts in rat livers pre-treated with ethanol, phenobarbital or 3-methylcholanthrene, respectively. In conclusion, no p-DCB DNA adducts were found either the in vitro or in vivo studies. In this study, we demonstrated that p-DCB is not genotoxic.