The inhibition of formation of Reactive Oxygen Species (ROS) was evaluated in human polymorphonuclear (PMN) cells. The DCF-DA mean fluorescence intensity in the cells was proportional to the oxidative damage. Untreated cells served as a baseline for oxidative activity in the absence of oxidative stress. The presence of BC fractions MTB and CW led to inhibition of the spontaneous ROS production in the cultures (A). H2O2 was used to induce oxidative stress in the cultures. Cultures treated with H2O2 in the absence of GBC30 fractions served as a positive control for ROS formation. Cultures treated with GBC30 fractions MTB and CW in the presence of oxidative stress showed reduced ROS formation compared to cultures treated with H2O2 alone (B). Data reflect averages of cultures performed in quadruplicate for each test condition. The data shown are representative of three independent experiments performed on PMN cells from different donors.