Griffiths (13) has presented evidence indicating that the browning reactions of banana fruit result from the enzymic oxidation of dopamine (3,4 dihydroxyphenylethyliamine) by polyphenoloxidase. Although dopamine does occur in various fruits and vegetables (23), it has not previously been implicated as an important substrate in browning reactions. The present investigation was undertaken to develop methods for preparation of banana polyphenoloxidase (PPO)3 and to determine some of its properties in comparison with phenol oxidases from other sources.