Laccase. purified from Coriolus versicolor, removed pentachlorophenol (PCP) from solution at pH 5, depending on initial PCP concentration and amount of Laccase. With 100 units of laccase, 100% of 25 mu g ml(-1) PCP and 60% of 200 mu g ml(-1) PCP were removed respectively over 72 h. No free chloride was released in the reaction. In reaction with 100 mu g PCP, products were primarily polymers (about 80,000 MW) with only 2-3 pg of o- and p-chloranils formed. Polymers were stable to acid hydrolysis and no release of PCP, or other low-molecular-weight products, was detected over several weeks. Laccase has a potential use in the biotreatment of aqueous effluents containing PCP: with polymerised products being removed from solution due to their high molecular weight.