Genotoxic chemicals not only damage cellular DNA, but may also induce cell apoptosis if they are lethal to the cell. p53, Bcl-2 and Bax play important roles in the regulation of genotoxic chemical induced cell apoptosis. Since the mechanisms by which cellular DNA damaged by different DNA-damaging chemicals may not be the same, we studied the involvement of p53, Bcl-2 and Bax in apoptosis induced by methyl methanesulfonate (MMS) and hydrogen peroxide (H2O2). H2O2 damages DNA by free radical generation and MMS damages DNA by DNA methylation. At non-lethal doses, both H2O2 and MMS induced high level of p53 protein accumulation. Nevertheless, while the amount of p53 protein increased with the dose of MMS and the occurrence of apoptotic cell death events, H2O2 doses that induce cell apoptosis attenuated the p53 protein accumulation level. Lethal MMS treatment also increased Bax, but not Bcl-2 expression, whereas in H2O2 induced apoptosis, the level of both Bcl-2 and Bax declined. These results indicate that toxic chemicals differentially regulate the accumulation of p53 protein. Thus, the pathways of toxic chemicals induced cell apoptosis are different and independent.