The use of peroxidase and catalase in electrochemical sensors for hydrogen peroxide is reported. The enzymes are chemically immobilised on nylon net. The peroxidase enzyme electrode is used in a flow injection analysis (FIA) mode as the working electrode in a three-electrode modified Stelte cell with hexacyanoferrate(II) as the redox mediator in a phosphate buffer carrier stream. The low potential used (– 100 mV versus silver-silver chloride) helps to offset the effect of redox-active interferents. The catalase enzyme is used in conjunction with a Yellow Springs Instruments Model 5739 oxygen electrode and has been studied in the dip mode at high pH. The two electrode systems can be calibrated between <10^–5 and >10^–3M hydrogen peroxide and do not suffer from interference by many of the components commonly found either in industrial samples where hydrogen peroxide is employed, or in wastewater samples.