Low density lipids of the atherosclerosis-unaffected human aorta, unlike plasma lipoproteins belonging to the same class, contain lipid peroxidation products in the superficial layer. The viscosity of the lipid phase of the aorta and blood plasma is the same. In protein of aorta lipoproteins, tryptophan residues are outside the particle whereas in plasma lipoproteins, they are buried deep in the lipid phase. The data on energy transfer to the probes provide evidence in favour of the fact that in aorta lipoproteins, protein is lying on the particle surface in a thicker layer and occupies a 2-times lesser area than in plasma lipoproteins.