Preliminary studies were made of the potential use of a membrane-immobilised enzymatic method for the treatment of p-cresol-containing wastewater. The enzyme polyphenol oxidase was immobilised onto hydrophobic polyethersulphone capillary membranes and hydrophilic nylon flat-sheet membranes, by adsorption, and by adsorption with glutaraldehyde cross-linking, respectively. It was found that the intermediate product of the polyphenol oxidase reaction, 4-methylcatechol, was detected when the enzyme was immobilised on the nylon membranes or was not immobilised, but only the o-quinone final product was detected when polyethersulphone was used as the immobilisation matrix.