The effects of 1-benzylimidazole on the expression of microsomal epoxide hydrolase (mEH) gene were examined in rat. Immunoblot analyses showed that hepatic microsomes isolated from rat treated with 1-benzylimidazole at 25, 50 or 100 mg/kg/day for 3 or 6 days exhibited 2-3-fold increases in mEH levels, relative to control microsomes. Northern and slot blot analysis revealed that 1-benzylimidazole is effective in increasing hepatic mEH mRNA levels at 24 h post-treatment (i.e. 4-5-fold). Hepatic mEH mRNA levels were elevated from 4-4- to 8-fold following 1-benzylimidazole administration in a time-dependent manner. These results demonstrated that 1-benzylimidazole induces mEH protein in rat and that the induction is primarily associated with accumulation of mEH mRNA levels.