"Brown rot caused by Monilinia laxa is an important fungal disease of apricot (Prunus armeniaca) causing economical losses in different growing areas in Europe. M. laxa induces great damage in apricot, attacking flowers, leaves, stem, branches and fruits. The damage severity is strictly related to the climate conditions and several fungicide treatments are often necessary in order to limit the disease. Therefore, the aim of this study was to investigate the changes in the content of pigments (chlorophylls, carotenoids), total polyphenols, peroxidase, catalase, polyphenol oxidase in the leaves of the different apricot varieties. All these parameters were chosen taking in account their involvement in plant disease resistance. Concerning to chlorophylls and carotenoids level, less amounts were recorded in the leaves collected from the all symptomatic apricot varieties studied. Activities of peroxidase, catalase and polyphenol oxidase and total polyphenols were increased in the apricot samples affected by M. laxa compared with the healthy ones. Among the analyzed cultivars, Dacia, Litoral and Favorit showed a great tolerance to M. laxa. The genotypes like Carmela and Viorica showed different susceptibility. IN RESISTANCE TO MONILINIA SPP."