Electrochemical oxidation of acetaminophen has been studied in the presence of glutathione and acetylcysteine. Our results indicate that N-acetyl-p-benzoquinone-imine (NAPQI) participates in a catalytic reaction with glutathione and N-acetylcysteine. Also, the observed homogeneous rate constants of the reaction of NAPQI with glutathione and acetylcysteine were estimated.