Polyaniline polyacrylonitrile composite films prepared by in situ electropolymerization of aniline on polyacrylonitrile-coated platinum electrode were used to immobilize polyphenol oxidase forming an enzyme biosensor. The novel polyphenol oxidase-based biosensor exhibited high sensitivity, low background and excellent stability, which showed no loss of activity after 100 consecutive measurements and intermittent usage for six months with storage in a phosphate buffer at 4degreesC. The construction parameters of the enzyme electrode were optimized. The influences of pH and temperature on the biosensor response were explored. The sensitivities of the enzyme electrode for catechol, phenol, p-cresol and m-cresol were 2.03, 0.96, 1.38 and 1.5 A M-1 cm(-2) respectively.