The use of model systems containing purified anthocyanins, chlorogenic acid (CG), and blueberry polyphenol oxidase (PPO) and of different analysis methods (HPLC and polarographic methods) have allowed the study of the mechanism of anthocyanin degradation by PPO. Cyanidin 3-glucoside (Cy 3-glc) was not oxidized by PPO since no molecular oxygen was consumed. However, the presence of CG induced pigment degradation. The quinone of CG, formed enzymatically, was involved in the degradation of Cy 3-glc by coupled oxidation mechanisms with partial regeneration of CG. This means that part of the CG was incorporated into the degradation products of Cy 3-glc. The ratio of degraded Cy 3-glc to oxidized CG was equal to 2. An anthocyanin degradation mechanism is proposed.