The differential effects of various fatty acids such as n-3 and n-6 types or degrees of unsaturation on the CYP2E1 induction and the production of lipid peroxidation (LPO) were investigated. The CYP2E1-transduced human hepatoma HepG2 cells (E47) were cultured in RPMI 1640 media containing different concentrations of various fatty acids up to 48 h incubation compared to 04 cells and CYP2E1-null cells. Treated fatty acids were linoleic acid (LA:n-6, C18:2), arachidonic acid (AA:n-6, C20:4) and docosahexaenoic acid (DHA:n-3, C22:6). The cell survival rate was decreased corresponding to the degree of unsaturation (LA>AA $cong$DHA) and to LPO production in E47 and 04 cells. The four or five unsaturation degree of fatty acids, AA and DHA, caused time- and dose-dependent cell death in E47 cells but not as much as in C34 (without CYP2E1), suggesting an important role of CYP2E1 in the DHA mediated damage. In the levels of lipid peroxides (LPO), AA also elevated LPO by 3- and 5- fold compared to DHA or LA treated E47 cells. However, AA did not increase LPO until 48 h incubation in C34 cells. In conclusion, the polyunsaturated fatty acids induced CYP2E1 induction might be changed by the elevated levels of lipid peroxide (LPO) and oxidative stress through the connection of CYP2E1 and degrees of unsaturated fatty acids.