The peroxidation of human erythrocytes induced by peroxyl radical initiator and its inhibition by several gallate esters (e.g., propyl, methyl, ethyl) and Trolox (a more polar analogue of vitamin E) have been studied. The antioxidant activity was determined on erythrocytes against hemolysis generated by a thermal activator, 2,2'-azobis-(2-amidinopropane)dihydrogenchloride. It was found that propyl gallate and its two analogues were more effective than Trolox in preventing cell lysis. However, the combination of gallate esters and Trolox produced a protective effect exceeding the arithmetic sum of their individual contributions. These perceived synergisms occur at more than one level of Trolox at a given level of a gallate ester.