Insecticides are the chemicals widely used in agriculture, environmental health, human-and animal-health fields. Exposure to insecticides has been associated with many hazardous effects, including antioxidative metabolism. In the current study, the effect of cypermethrin (CYP), propetamphos (PRO) and their mixtures on oxidative stress in mice to understand the possible health effects to animals and human beings was investigated. In the present study, 245 male Albino mice weighing 35-40 g were used. The mice were divided into seven groups. The first group served as the control group. The second and third groups were administered CYP at doses of 5 mg/kg/bw and 10 mg/kg/bw, respectively, and the fourth and fifth groups were given PRO at doses of 2.5 mg/kg/bw and 5.0 mg/kg/bw, respectively. The sixth and seventh groups received combination regimens containing 5 mg/kg/bw CYP plus 2.5 mg/kg/bw PRO and 10 mg/kg/bw CYP plus 5 mg/kg/bw PRO, respectively, in feed for 60 days. Blood samples were collected by cardiac puncture on the 15th, 45th and 60th days. Serum nitric oxide (NO) and plasma malondialdehyde (MDA) levels and erythrocyte superoxide dismutase (SOD), catalase (CAO, and glutathione peroxidase (GSH-Px) activities were measured. In conclusion, the alterations observed in the MDA and NO levels and SOD, CAT, and GSH-Px activities of the trial groups, demonstrate the administration of certain doses of CYP and PRO, either alone or combined, to mice for a period of 60 days to produce oxidative stress. The degree of oxidative stress was found to be related to the dose administered, the duration of exposure and the administration of the indicated compounds either alone or as a combination. (C) 2008 Wiley Periodicals, Inc.