In this study, Macrolepiota mastoidea, a wild edible mushroom, was evaluated for its polyphenol oxidase potential. Native electrophoresis, stained by L-dihydroxyphenylalanine, of the crude extracts from this species showed two bands having R-f values of 0.38 (minor) and 0.50 (major), supporting a polyphenol oxidase potential. The crude extracts showed monophenolase activity against 3-(4-hydroxyphenyl)-propionic acid and diphenolase activity against 4-methylcatechol as substrates. Monophenolase and diphenolase activities of enzyme extract prepared from M. mastoidea showed pH optimum values at pH 6.0 and pH 4.0, respectively. The extracts retained about 100% and 60% of their original monophenolase and diphenolase activities at their optimum pH values, respectively. It was estimated from thermodynamic data that M. mastoidea had a thermostable monophenolase activity. Thiourea and ascorbic acid were highly potential inhibitors for monophenolase, and ascorbic acid and sodium metabisulphite for diphenolase activity. It is clear from the present results that the enzyme extracts prepared from M. mastoidea possess polyphenol oxidase activities with interesting properties. (c) 2006 Elsevier Ltd. All rights reserved.