Three types of sensors for continuous determination of hydrogen peroxide (HP) are described. The working principles are based on the decomposition of HP by a catalyst and on the measurement of the amount of oxygen thereby produced. The change in oxygen tension is quantitatively determined via the quenching of the fluorescence of a silica gel-adsorbed dye entrapped in silicone rubber. Three methods were found to be useful for HP decomposition. In the first one, the enzyme catalase (which acts as the catalyst) is co-adsorbed onto silica gel and thus is in the same phase as the indicator. In the second one, the enzyme and the dye are adsorbed on different silica gel particles which then are incorporated into the polymer layer. In the third one, finely dispersed silver powder (another catalyst) is embedded in a silicone rubber layer that is spread over the oxygen sensing membrane. The sensor is capable of continuously recording HP in the 0.1 to 10.0 mM concentration range, with a precision of ±0.1 mM at 1 mM HP. Its response time varies from 2.5 to 5 min.