Although lipid peroxidation of biological samples may be assessed by different chemical and physical methods, those based on the measurement of malondialdehyde formed from the breakdown of endoperoxides during the last stages of the oxidation of a polyunsaturated fatty acid, appear as the most widely used. Among the various methods to evaluate malondialdehyde, which include direct spectrophotometry or high pressure liquid chromatography, the reaction with thiobarbituric acid to form a colored adduct appears as a more rapid, inexpensive and sensitive technique. This method, however, is subject to some interferences which, if not considered, may lead to erroneous results. The present review emphasizes the significance of malondialdehyde measurement in biological samples, the chemical conditions of its reaction with thiobarbituric acid and the different procedures to isolate and determine the malondialdehyde-thiobarbituric acid adduct.