Chlorpyrifos is an organophosphorus insecticide that is applied extensively for pest control. L-arginine is an α-amino acid that is crucial in protein biosynthesis. An investigation was carried out to determine the impacts of L-arginine on the hepato-renal indices of rats treated with chlorpyrifos. Thirty-five (35) rats were used and they were allocated into five groups of seven rats each. They received the following treatments by oral gavage for 28 days: distilled water, olive oil (1 ml/kg), chlorpyrifos (8.5 mg/kg), L-arginine (100 mg/kg), chlorpyrifos (8.5 mg/kg) and L-arginine (100 mg/kg). The rats were euthanized after the study ended and the hepatorenal indices were evaluated. The gamma glutamyl transferase activity of the chlorpyrifos group significantly increased (p < 0.05). Additionally, chlorpyrifos induced significant reduction in the activities of hepatic superoxide dismutase, renal catalase and renal glutathione peroxidase. Conversely, L-arginine significantly increased the activities of hepatic superoxide dismutase, renal catalase and renal glutathione peroxidase both alone and in combination with chlorpyrifos. From these results, it may be deduced that L-arginine has potential bioprotective and antioxidant effects against chlorpyrifos.