Abstract: The electrochemical detection of H2O2 (at pH 2 to 8) by graphite (RW 0 and RW 1, from Ringsdorff Werke GmbH) and carbon (RW 2) electrodes modified with a catalyst layer of vacuum-deposited Pd - Au was studied by using a flow injection analysis system. The graphite and carbon modified electrodes were more effective amperometric sensors than was a vitreous-carbon electrode and overvoltages could be decreased by 800 mV. At least 200 .ANG. of catalyst was necessary to obtain a fully catalytic electrode. Rectilinear calibration graphs were obtained for 0.1 µM to 1 mM H2O2.