When storaging the plum fruits of the varieties Stenley under normal atmospheric conditions and by the method of treating them with the synthetic inhibitor of ethylene Fitomag, the modification of peroxidase and polyphenol oxidase activity in fruits depended on the conditions and duration of storage, metabolic processes course in fruit during storage, the particularities of the varieties and their storage methods. The gradual decrease in peroxidase activity and the increase in polyphenol oxidase activity occurred in the case of fruit preservation by both methods. In the fruits storaged by the Fitomag method, the values of these enzymes were lower compared to those in the ordinary atmosphere. The lower intensity of the redox processes has beneficially influenced the preservation of the quality of the fruits preserved by this method compared to the usual atmosphere. There were also essential differences between the control and the variants treated with SBA Reglalg and microelements, as well as between varieties.