Effects of deltamethrin on lipid peroxidation were investigated for subacute. subchronic and chronic periods. Deltamethrin was given to Swiss Albino mice at 1.5, 2.5, or 7.5 mg/kg. Lipid peroxidation was evaluated by determining malondialdehyde (MDA) levels in plasma, and determining glutathione peroxidase (GSH-Px), superoxide dismutase (Cu-Zn SOD) and catalase activities in erythrocytes on days 15, 45, and 60. MDA levels increased in deltamethrin dosed groups, especially for the subchronic and chronic periods. GSH-Px, Cu-Zn SOD and catalase activities in erythrocytes were decreased at high doses of deltamethrin, especially at the high dose (7.5 mg/kg) deltamethrin group.