One of the problems in the handling and processing of various kinds of fruits, is the enzymatic and nonenzymatic browning. The polyphenoloxidases are strictly related with the first aspect, needing therefore, more attention from the scientists and food industries. These enzymes oxidize mono, di and polyphenols in the presence of molecular oxygen, producing dopachromes which are polymerized to melanins as a final product. Their mechanism of action, however, is still unknown. The purpose of this article is to provide specific information as to the nature and behavior of the polyphenoloxidases found in different kinds of fruits and foods.