The scientific research was carried out on the leaves of two varieties of plum, one of local origin - Superprezident and the second of foreign origin - Stenley. In the leaves was determined the activity of the enzymes peroxidase and polyphenol oxidase. The activity values of the enzymes investigated during the vegetation period changed depending on the metabolic processes that took place in certain phenophases, the environmental conditions (t0, humidity, etc.), the biological characteristics of the varieties and the substances used to treat of the plum trees. In the treated version of plum trees with SBA Reglalg substances and of the microelements B, Zn, Mn, Mo, the activity of these enzymes was higher than in the control variant. The mentioned substances positively influenced the activity of these enzymes in ontogenesis, which played an important role in the metabolic processes, contributing to the increase of the productivity, the quality of the fruits and the resistance of the plum trees.