This study was intendent to examine if N-acetylcysteine (NAC) changes liver GSH levels and influences ChE serum activity in rats intoxicated with chlorfenvinphos. The studies were conducted on male Wistar rats of 200±20 g body weight. One group of rats was pretreated with 0.1% water solution of NAC. NAC was administered in drinking water 24h before intoxication. The control groups received oil intragastrically by stomach tube in the amount of 0.1ml/100g (I), immediately or after NAC pretreatment. The experimental groups received oil solution of chlorfenvinphos in a dose of 0.02 LD50 or 0.1 LD50 immediately or after pretreatment with NAC. One and 24 hours after intoxication with chlorfenvinphos (or after NAC pretreatment) the blood samples were collected and livers were quickly removed and placed in iced 0.9% NaCl containing 0.16 mg/ml heparin. ChE serum activity and GSH level were measured. The results of this study demonstrated the changes in serum ChE activity and liver glutathione levels in the rats after administration of chlorfenvinphos at single doses. The results reported here indicate that NAC influences a decreased level of GSH in the liver of chlorfenvinphos-intoxicated rats and does not prevent ChE inhibition.