Amylomyces rouxii eliminated 85% of initial pentachlorophenol (PCP) at 12.5 mg l(-1) when grown with 0.1 g tyrosine l(-1), but only 55% without tyrosine. Addition of tyrosine in the culture medium increased the monophenolase activity by 1.8-fold. Tyrosinase is thus indicated to be the phenoloxidase involved in PCP degradation by A. rouxii.