The electrochemical oxidation of H2O2 at platinum rotating disc electrodes and microelectrodes was studied in the presence of chloride in the range 0-120 mM at pH 7.3. Oxidation was inhibited by chloride with greater inhibition at higher electrode rotation rates. The mode of inhibition was deduced to be non-competitive with the chloride interacting with precursor binding sites at the electrode surface, since increased [H2O2] did not decrease the degree of inhibition. The rotation rate dependence indicates that it is likely a soluble platinum complex involving chloride forms to remove binding sites from the electrode surface.