The phenol oxidase of a monogenean, Paramazocraes thrissocles, oxidizes phenolic amines more effectively than other phenols studied. Based on the substrate specificity, the probable substrate for eggshell formation has been suggested. The enzyme shows the pH optimum of 7–2. At 40°C it shows maximum activity. Proenzyme is activated by metal ions and detergents. Copper chelating compounds strongly inhibit the enzyme.