The purpose of this investigation was to establish the antioxidant effect of flavonoid epicatechin (EC) a low concentration (0.75 muM). The relative antioxidant potentials were measured against radicals generated by tert-BOOH in isolated rat hepatocytes and calf thymus DNA. EC is an effective antioxidant, it completely prevents tert-BOOH induced oxidation and thereby prevents subsequent lipid peroxidation. It also plays an important role in conserving of endogenous antioxidants such as GSH and catalase. As it is a radical scavenger, it is a prominent antioxidant on calf thymus DNA exposed to tert-BOOH. Oxidative stress induced by tert-BOOH at different concentrations in these isolated cells led to lipid peroxidation and changes in endogenous antioxidant levels, which were prevented by EC at a dose of 0.75 muM. (C) 2002 Elsevier Science Ltd. All rights reserved.