The electrochemical oxidation of tyrosine has been studied on polycrystalline and (111) single crystal platinum electrodes in 0.1 M HClO4. No surface sensitivity of bulk tyrosine reactions has been detected for these two electrodes, although the adsorption process seems to be structure-sensitive. The onset for tyrosine electrooxidation is observed at ca. 0.7 V for both surfaces. In situ FTIR technique was used to discern the nature of the products formed during the oxidation processes. The early stages of tyrosine oxidation occur via a decarboxylation to carbon dioxide. Two complex parallel reactions were found at E > 1.10 V vs. RHE: one of them leading to a gamma-lactone of hydroxy-substituted benzofurane, and the second with the formation of p-benzoquinone. The assignment of these products is based on the corresponding transmission spectra. (c) 2005 Elsevier B.V. All rights reserved.