Abstract Phenols in tea are responsible for its antioxidant activity. The pure catechins and phenolic acids found in tea are more powerful than the antioxidant vitamins C, E and β-carotene in an in vitro lipoprotein oxidation model. Comparison of the tea fractions indicated that both catechins and theaflavins contribute to the teas' antioxidant characteristics. Black and green teas were not significantly different in phenol content, in antioxidant strength as measured by IC 50 , or in antioxidant potential as measured by the phenol antioxidant index (PAOXI). The PAOXI of teas was significantly higher than grape juices and wines. Tea catechins and both green and black tea exhibited potent lipoprotein-bound antioxidant activity. Phenol antioxidants from tea were calculated to be a large source of antioxidants in the U.S. diet.