A method suitable for commercial application was developed for the partial purification of apple polyphenol oxidase (aPPO) from apple (Malus pumila L Bramley＇s Seedling). The yield of aPPO extracted from leaf tissue was greater than that from fruit. The aPPO was extracted from apple leaf tissue in a phosphate buffer at pH 7 (20 mM) containing 5.0 mi l(-1) Triton X-100 and 2.5 g l(-1) polyvinylpyrrolidine (PVP). The extract was clarified by centrifugation or by standing for a period of 2 weeks. The aPPO was subsequently purified 50-fold by the sequential use of DEAE-Sephadex and ultrafiltration. The DEAE-Sephadex was applied as a preswollen batch with its use optimized for recovered specific activity of aPPO and cost. Using phloridzin and I-methyl catechol as substrates, the partially purified aPPO had specific activities of 0.089 and 4.9 mu kat mg(-1), respectively, and K-m values of 0.6 and 3.6 mM, respectively. Recovery of phloridzin hydroxylase activity relative to DEAE-Sephadex was 3.3 mu kat g(-1) and relative to apple leaf tissue (following purification) was 8.0 nkat g(-1).