Lipid peroxides are the products of chemical damage done by oxygen free radicals to the polyunsaturated fatty acids of cell membranes. This test is an assay of total thiobarbituric acid-reactive substances (TBARS) in serum using HPLC. The HPLC separation step isolates the TBARS from potential interfering compounds that can give false elevations in a simple colorimetric assay. The results provide a measure of total serum lipid peroxidation, an indicator of whole body free radical activity. High levels of lipid peroxides are associated with cancer, heart disease, stroke, and aging.