Chloroperoxidase from Caldariomyces fumago was applied for the oxidation of indole to oxindole using hydrogen peroxide as the oxidant in aqueous t-butyl alcohol medium. Different ways of adding the oxidant, various reactor types, and the use of a hydrogen peroxide-stat were compared, resulting in a 20-fold increase of the total turnover number (ttn) and space-time yield (sty). The highest ttn of >860,000 was obtained in a fed-batch reactor, whereas the highest sty of 120 g/(L.d) was reached in a continuously operated enzyme membrane reactor. The results were compared to other enzyme systems already established for the synthesis of amino acids and carbohydrates.