High density lipoproteins (HDL), also called alpha lipoprotein, are small high protein content particles that are present in the vascular and extravascular systems. Two main classes of HDL, HDL2 and HDL3, have been identified and found to have different structures and different metabolisms. Their principal function is to ensure that tissue cholesterol returns to the liver. HDL, and notably HDL2, are factors that protect against cardiovascular diseases. HDL2 are subjected to the influence of numerous dietetic, genetic and hormonal factors, while HDL3 seem to be more independent of all variations, except those of alcohol.