Introduction: Oxidative modifications of Low-Density Lipoprotein (LDL) particles are of great interest in atherosclerosis research. Such modifications are known to generate a number of fragments with different biological properties, including increased uptake by macrophages, cell activation and toxicity. Most of the experimental and clinical works based on in vitro oxidized LDL have employed Cu- and, to a lesser degree, Fe-ions as oxidation mediators. The mechanisms by which these ions can both initiate oxidative reactions and generate the end products are not fully understood. Several techniques to characterize the oxidative state of LDL are available. Such techniques include UV absorption by conjugated dienes, separation of fragments by high performance chromatography, detection of TBARS generated during the oxidation process, and changes in Z-scan signal by photothermic spectroscopy (Gomez et al, Chemistry and Physics of Lipids, 2004, 132: 185-95).  Objective: The present work was aimed at the separation of products in metal ion-treated LDL preparations, and their characterization by photothermic spectroscopy. We have thus studied the products of Cu2+- and Fe2+-initiated modifications in LDL using size-exclusion chromatography and Z-scan technique.  Materials and Methods: Human purified LDL was obtained by sequential ultracentrifugation and the samples were treated with either CuSO4 (20 μM/mg protein, 18 h, 37 ºC) or FeSO4  (1 μM/mg protein; 48 h, at room temperature) according to stablished protocols. The treatment reactions with metal ions were stopped by addition of EDTA (0.5 mM).  Results: The products of both treatments exhibited different degrees of fragmentation as detected by size-exclusion chromatography (FPLC, Superdex-200). These differences were also accompanied by changes in the Z-scan signal.  Conclusion: The metal-initiated modifications in LDL lead to the appearance of products that have different properties and may play distinct roles in the atherosclerotic process.