The present invention provides a method of carrying out an oxidation reaction catalysed by a monooxygenase enzyme and using hydrogen peroxide as an oxidant, in which reaction a low level of oxidation damage of the monooxygenase occurs, said method comprising producing the hydrogen peroxide simultaneously with the oxidation reaction, wherein the hydrogen peroxide is produced at a rate less than or equal to the rate at which it is used in the reaction or said method comprising carrying out the reaction in the presence of an H2O2 or hydroxyl radical sequestering agent that controls the H2O2 or hydroxyl radical concentration.