The research in progress and proposed has the objective of measuring the kinetics of free radical oxidation in model lipid bilayers and in natural membranes in order to develop some quantitative relationships between lipid structure and organization and susceptibility both to radical oxidation and to inhibition by natural and synthetic antioxidants. The experimental program involves generating free radicals at known rates initially in model lipid systems and eventually in natural cell membranes, characterizing the kinetics of free radical oxidation in these systems and finally observing the effects of various antioxidants on the oxidation kinetics. Conclusions will be drawn based on experimental data interpreted with reference to the large body of physical organic chemical data available on free radical oxidation reactions.