A simple technique using a low flow gas meter is described for the off-line and on-line measurement of hydrogen peroxide. The volume of oxygen produced from the reaction of the enzyme catalase with hydrogen peroxide was followed. A linear correlation was demonstrated between total O2 evolution and H2O2 concentration in the range 0.25-1.5% for on-line assays and 25-500 mg/l and 0.38-3% for the off-line method. A response time of 17 min was obtained for the off-line for hydrogen peroxide concentrations of 25-500 mg/l. The response time of an on-line version of the method was approximately 5 min for hydrogen peroxide concentrations of 0.25-1.5%. The technique was not significantly temperature sensitive in the range 25-45°C. Copyright (C) 2000 Elsevier Science Ltd.