DANIELA IONESCU, ANCUTA IOANA ISAIA (OARCEA), MIHAI GAFENCU, SORIN BOLINTINEANU, ADINA CATA, DANIELA BRATOSIN, LAVINIA TOADER, IOANA MARIA CARMEN IENASCU EVALUATION OF ANTIOXIDANT CAPACITY OF PLANT EXTRACTS USING FLOW CYTOMETRY This study is aimed to evaluate the inhibitory effect of natural extracts on reactive oxygen species (ROS) in human red cells (RBCs) under oxidative stress and to demonstrate the importance of using natural extracts from plants in the fight against oxidative stress. Therefore, seven nonalcoholic extracts were tested at several dilutions, in order to prove their antioxidant activity using flow cytometry. The level of intracellular hydrogen peroxide significantly decreased when the cells were coincubated with different extracts, the values of the Mean Fluorescence Intensity (MFI) ranging from 206 to 3702, compared with 3872, the value obtained in case of H2O2-treated cells (RBCs + H2O2). All the tested extracts demonstrated a good inhibition, Melissa officinalis L. extract showed a greater percentage of hydrogen peroxide inhibition even at the last dilution (94.70% (D-a)….85.76% (D-e)). The results suggest the importance of the investigated natural extracts to combat oxidative stress.