D/H exchange occurs during the electroreduction of ethanol at polycrystalline platinum. Methane and ethane presenting different degrees of D/H exchange were observed employing CD3-CH2OH and CH3-CD2OH. Using CH3-CD2OH, total exchange takes place during the formation of ethane from both adsorbed and bulk ethanol. For the methyl labelled compound CD3-CH2OH, a total exchange was observed during the production of methane from adsorbates, but only partially in the case of ethane. The results are consistent with the nature of the adsorbed residues of ethanol proposed in a recent publication. In situ Fourier Transform ir (FTir) analysis of the adsorption products confirms the isotope exchange reactions.