LDL (low density lipoproteins) are complexes of a single molecule of apoprotein B-100 (apoB-100) non-covalently associated with triacylglycerol, free cholesterol, cholesterol esters, and phospholipids. LDL complexes contain single molecules of apoB-100, but their content of lipids is variable (Chapman et al. 1988; Mateu et al. 1972; Tardieu et al. 1976). High levels of LDL in the blood are strongly correlated with increased risk of atherosclerosis, and recent studies have raised the possibility that this risk is further increased in individuals whose blood LDL population is enriched in high-density (low lipid content) LDL complexes (Rizzo and Berneis 2006). The LDL complex annotated here contains an average lipid composition.