The subtractively normalized interfacial Fourier transform infrared spectroscopy (SNIFTIRS) has been used to examine an oxidation product from adsorption of the enzyme, ribonuclease A, at the platinum electrode. At potentials of 600 mV (SCE), a negative going peak due to the formation of the oxidation product CO2 was clearly visible with both s- and p-polarized IR beams. This gives evidence that adsorption of the protein occurs through the carboxylate groups of the acidic residues of the protein at anodic potentials with subsequent oxidation occurring by a decarboxylation mechanism.