We examined the possibility of developing a risk assessment method for potentially hazardous chemicals by using catalase mutant strains. These strains were constructed by transforming plasmids encoding the catalase cDNA from catalase mutant mice (Csb, Csc) and its corresponding wild type (Csa) into catalase-deficient Escherichia coli UM255. Their catalase activities were in the following orders: Csa>Cs c>Csb>UMZSS, whereas their susceptibilities to H2O2 were UM255>Csb>Cs c>Csa. Chemical-induced cytotoxicities, such as hydroquinone and some inorganic heavy metals, were examined by a growth inhibition assay. The inhibition for bacterial growth was determined by measuring the diameter of the inhibitory zone. We found that the susceptibilities of UM255, Csa, Csb and Csc strains to various chemicals negatively correlated with their catalase levels, suggesting the involvement of H2O2 in the processes of chemical- induced cytotoxicity. The results support the usefulness of these newly established strains for hazard identification of oxidative chemicals in a risk assessment process.