Polyphenoloxidase (PPO), isolated from Anethum graveolens L, showed activity on catechol, L-tyrosine and DL-DOPA. The optimum pH for the PPO was 7.0. Heat inactivation studies showed that heating for 40 and 15 min at 60 degrees and 80 degrees C, respectively, caused a 50% loss in enzymatic activity. The enzyme catalysed browning reaction was significantly inhibited in the presence of ascorbic acid, 2-mercaptoethanol, uric acid and barbituric acid. The most effective inhibitors were ascorbic acid and 2-mercaptoethanol.