Malondialdehyde (MDA) levels in infant milk formulas have been monitored by using an aqueous acid extraction method combined with the thiobarbituric acid method (TBA-test). Vegetable oils, with a remarkable content of polyunsaturated fatty acids (PUFA) are used to enrich the infant milk formulas. As PUFA are more susceptible to autoxidation, it becomes of great interest to have information about the safety and preservation of these products. We monitored MDA content in twenty of the most popular infant milk formulas and in some commercial cow milk samples and compared the obtained data. Levels of MDA ranged between 200 and 1200 ppb: all values but one were higher, up to five times, than those found in cow milk samples. To evaluate the accuracy of the data obtained from the TBA-test, some samples were also analyzed with an HPLC derivative method: preliminary results show a good agreement between the two analytical techniques.