Nitric oxide (NO) is a free radical species that diffuses and concentrates in the hydrophobic core of lowdensity lipoprotein (LDL) to serve as a potent inhibitor of lipid oxidation processes. Peroxynitrite (PN), the product of the diffusionlimited reaction between NO and superoxide (O2), represents a relevant mediator of oxidative modifications in LDL. The focus of this review is the analysis of interactions between NO and PN and its secondary reactions with oxygen radicals on LDL oxidation, which are relevant in the development of the early steps as well as progression of atherosclerosis. We propose that the balance between rates of PN and NO production, which greatly depends on oxidative stress processes within the vascular wall, will critically determine the final extent of oxidative LDL modifications leading or not to scavenger receptormediated LDL uptake and foam cell formation.