The electrochemical oxidation of H2O2 at a platinum rotating disc electrode was studied at pH 7.26 for the [H2O2] range 0-70 mM, rotation rates 630-10000 rpm and anodic potential + 264 to + 712 mV vs Ag/AgCl using staircase potentiometry. A mechanism is proposed to account for the steady-state current as a function of rotation rate, [H2O2] and anodic potential. This mechanism involves reversible binding of H2O2 to electrochemically generated Pt(II) surface sites, reduction of the site and inhibiting competitive adsorption of H+ and O-2. Potential-invariant values of the constants for H2O2, H+ and O-2 binding are determined and the rate constants for the reduction and the re-oxidation of the binding site as a function of potential are evaluated.