We have assesed the actions as free radical scavengers and inhibitors on peroxidation of hesperidin and neohesperidin dihydrochalcone, two flavonoids, flavanone and dihydrochalcone respectively, as some of the pharmacological properties of flavonoids group have been related with these activities. Hesperidin just at 10(-4) and 5 · 10(-4)M is able to show a low inhibitory activity in the superoxide anion radicals (O(2)(-)) genesis (8.66 ± 1.40 and 11.69 ± 2.36% respectively), and on the non-enzymatic lipid peroxidation at 10(-3)M dose (9.78 ± 0.35%), without affecting the hydroxyl radical (•OH) formation, generated by the ascorbic acid-Fe(3+)-EDTA system. In the other hand, neohesperidin dihydrochalcone is an authentic antioxidant drug as tested at all doses. It showed a great scavenger activity and/or inhibition of formation on O(2)(-) radicals (31.53 - 84.62%) and a significant scavenging effect on OH radicals (6.00 - 23.49%), as well as an important inhibitory action on non-enzymatic lipid peroxidation (15.43-95.33%).