The oxidation of LiAsF6/acetonitrile and LiClO4/acetonitrile solutions containing 0.003-0.05M H2O was studied on platinum and glassy carbon electrodes by in situ Fourier transform infrared spectroscopy. Both the solvent and the solute are unstable at potentials positive to ca. 2.2 V vs. SCE. The main oxidation product is CO2. Other products detected are : acetamide (LiAsF6/acetonitrile), ClO2, and an unspecified "nitrogen oxide" (LiClO4/acetonitrile). Carbon dioxide is formed via a reaction of acetonitrile with trace water as substantiated by the occurrence of an isotopic shift of the CO2 stretching vibration when using (H2O)-O-18. The rate of the CO2 formation is increased by the presence of perchlorate anions and the Pt surface.