The antifouling (AF) potential of hydrogen peroxide (H2O2) produced enzymatically in a coating containing starch, glucoamylase, and hexose oxidase was evaluated in a series of laboratory tests and in-sea field trials. Dissolved H2O2 inhibited bacterial biofilm formation by eight of nine marine Proteobacteria, tested in microtiter plates. However, enzymatically produced H2O2 released from a coating did not impede biofilm formation by bacteria in natural seawater tested in a biofilm reactor. A field trial revealed a noticeable effect of the enzyme system: after immersion in the North Sea for 97 days, the reference coating without enzymes had 35-40 barnacles, 10% area coverage by diatoms and 15% area coverage by tunicates. The enzyme containing coating had only 6-12 barnacles, 10% area coverage by diatoms and no tunicates. The enzyme system had a performance similar to a copper-based commercial coating and thus appears to have potential as a non-persistent AF agent.