Vitamin E usually works as a biological antioxidant, preventing the oxidation of polyunsaturated fatty acids and proteins, for which it is considered an important protective factor in the development of diseases related to oxidative processes. Beyond its antioxidant properties, it has been involved also in genetic expression, mitochondrial metabolism, cell differentiation and immune system regulation. From the point of view of its antioxidant protection properties, values > or = 1200-1300 micrograms/dL are considered optimum levels (standardized according to plasmatic lipid levels). In relation to the beneficial advantage effects of vitamin E on primary or secondary atherosclerotic disease, data are not conclusive. Vitamin A is part of the organism's defense barrier against free radicals. Its antioxidant mechanism of action includes scavenging of single oxygen and thiol free radicals, and it also could be related to processes that involve genetic expression and cell differentiation. As an antioxidant, vitamin A plasmatic levels > or = 80 micrograms/dL are considered optimal. The highest risk of using this vitamin is related to its acute or chronic toxicity. Quantification of serum vitamin E (alpha tocopherol) and vitamin A (retinol) are made by high performance liquid chromatography (HPLC), method of high precision, sensitivity and reproducibility.