The results show support for concern about extrapolating data to humans, given the degree and forms of exposure to these kind of compounds. In this study the authors aimed to evaluate the oxidative stress enzymes indicative of liver damage in rats exposed to M (malathion) acute and chronic forms using C (cimetidine) and cimetidine plus malathion (M + C). Malathion, widely used organophosphorus insecticide worldwide, induces oxidative liver damage type; Cimetidine is an antagonist of histamine H2-receptor, it has been shown to be an inhibitor of various CYP450 isoforms. Male Wistar rats weighing 200-250 g were studied, exposed to malathion orally for 3 weeks (0.15 mg/kg/day, 2 mg/kg/day, 15 mg/kg/day) and cimetidine 10 mg/kg/day. Malathion affects susceptibility to oxidative stress and possibly modifies the antioxidant defense capacity directly or indirectly.