The biochemical properties of polyphenoloxidase (PPO) from Lerman and Fuerte avocado varieties, which differ in their rates of browning, were studied. The partially purified PPO from either source had a pH optimum around 5.5–6.5 and was characterized by a relatively high stability to heat. PPO of Lerman and Fuerte avocado exhibited fairly similar substrate specificity, with a higher activity toward 4-methyl catechol, pyrogallol or dopamine and a lower one toward catechm, caffeic acid or chlorogenic acid. No lactase or cresolase activity was detected with either enzyme. The effect of several types of PPO inhibitors was tested and it was found that, with minor exceptions, the two enzymes responded similarly. PPO of both sources exhibited similar relative activities toward most of the o-dihydroxyphenols tested and, as reported earlier, similar isoenzyme patterns were obtained with DL-DOPA, caffeic acid, chlorogenic acid, and 4-methyl catechol. It can therefore be concluded that the higher rate of browning observed when freshly cut Fuerte is exposed to air, as compared with Lerman, is unlikely to result from a difference in the properties of the PPO enzymes in each of these varieties. Instead, it may be directly correlated to the amount of PPO activity present per gram wet weight and/or the concentrations of the natural substrates present.