Background and Aim: Organophosphate insecticides such as diazinon (DZN) can disrupt the body's antioxidant defense system. Antioxidants protect cells against oxidative stress.

In the present study, antioxidant properties of N- acetylcysteine (NAC) and vitamins E and C in reducing oxidative stress caused by DZN in rat spleen were compared.

Materials and Methods: In this experimental study,48 male Wistar rats were randomly divided into eight equal groups including. control ., DZN (100 mg/kg), NAC (160 mg/kg), vitamin E (150 mg/kg), vitamin C (200 mg/kg), NAC+DZN, vitamin E+DZN, and vitamin C+DZN groups. Twenty-four hours after intraperitoneal injection.the animals were anesthetized and their spleen tissues were quickly removed. After tissues’ hemogenation superoxide dismutase (SOD), catalase (CAT), glutathione S-transferase (GST) ,lactate dehydrogenase activities, as well as glutathione (GSH) and malondialdehyde levels were determined using biochemical methods.

Results: DZN increased SOD and GST activities , but it decreased CAT activity and GSH content in the spleen. Administration of the antioxidant NAC or vitamin E caused SOD and GAT improvement.

Conclusion: DZN induces oxidative stress in the spleen. NAC ,through increasing the synthesis of GSH , vitamins E ,and C- by removing free radicals- reduce DZN-induced oxidative stress. Comparing the effects of these antioxidants on GSH and GST activity indicates that the antioxidant value of NAC is greater than vitamins E and C.