It has been shown that the content of individual lipids and their ratio to phospholipids in blood lipoproteins of various density markedly differs in different classes of vertebrates, these differences being especially distinct for low density lipoproteins (LDL), as compared with high density lipoproteins (HDL2 and HDL3). Specifically, the total concentration of phospholipids and triacylglycerols in LDLs decreases in a sequence from fish to mammals, while the content of cholesterol esters increases, the proportion of cholesterol, cholesterol esters and triacylglycerols markedly increasing when calculated for phospholipids. Hence, it seems that the cholesterol coefficient of atherogenicity increases in the course of evolution of vertebrates. The HDL phosphatidylcholines contain much less fatty acid radicals with the odd number of carbon atoms than the cholesterol esters, this ratio being less distinct in fish as compared with birds or mammals. As a rule, domesticated animals have a higher cholesterol coefficient of atherogenicity than the wild ones, i.e., they are more susceptible to atherosclerosis.