Three different phenol oxidases produced by the basidiomycete fungus Pleurotus ostreatus have been isolated and their main structural, enzymatic and physico-chemical properties characterized. Studies have focused on the most abundantly secreted of these proteins, a copper-enzyme specific towards ortho-diphenol substrates. This protein was purified to homogeneity and part of its primary structure determined by direct protein sequencing. The influence of pH, temperature and presence of water-soluble or water-insoluble organic solvents on the activity and stability of the enzyme were also investigated. These data can be used for applying bioreactors to problems of environmental concern such as waste-water treatment.