Antioxidants which are peroxyl radical scavengers have been compared in a model of lipid peroxidation based on the oxidation of a suspension of linoleic acid initiated by a thermolabile azo compound. By analysing the effect of antioxidant concentration on linoleic acid peroxidation we have defined the constant kAH which characterises the rate of the reaction of the antioxidant with the peroxyl radical. This allows quantitative comparison of the efficiency of different antioxidants as peroxyl radical scavengers. By using an initiation system which is not iron dependent we were able to show that the iron chelators desferrioxamine, BW A4C and U74500A are also peroxyl radical scavengers. © 1989.