2-Thiobarbituric acid (TBA) test, as indirect method, has recently been used for the determination of lipid peroxidation in biological systems including blood. Together with the low sensitivity, lacks of the specificity and the understanding the reaction mechanism, however, have limited the usefullness of TBA test. Under the nitrogen atmosphere FeCl₃ showed great enhancement effect on the sensitivity of TBA reaction with serum protein precipitate involving lipid peroxides, but not with tetraethoxypropane. Thus ferric ion was thought to catalize the releasing TBA reactive chromogenic substance, malondialdehyde, from its precursors. The amount of ferric ion required seemed to be proportional to that of serum tested. Also, oxygen should be eliminated in serum TBA reaction so that the reaction could reach at stabe maximum and keep its plateau value. Under anaerobic atmosphere, albumin and amino acids (methionine and glutamic acid) may not contribute significantly to the great enhancement of serum TBA value induced by ferric ion.