Lipid peroxidation may be important in the pathogenesis of atherosclerotic cardiovascular disease, particularly in its earliest stages. Antioxidant vitamins may prevent or mitigate lipid per-oxidation. Most studies that assessed the effect of antioxidant vita-mins on lipid peroxidation relied on markers that are not specifically or directly related to in vivo processes. A common approach (thiobarbituric acid–reactive substances test) is to measure certain end products of lipid peroxidation, mainly malondialdehyde (MDA), which react with thiobarbituric acid under heat and acidic conditions. However, the specificity of this approach is limited. Another approach is to measure the susceptibility of harvested LDL to oxidation in vitro. The biological relevance of this in vitro approach is questionable.