It is planned to continue the structural studies on serum lipoproteins using enzymatic probes (proteolytic and lipolytic enzymes) in association with physical and chemical techniques. Particular emphasis will be placed on the molecular aspects of the re-assembly of high and low-density lipoproteins starting from its separated constituents and also employing lipids of biological or synthetic sources. In such studies, lipid-free polypeptides will be used as will fragments thereof obtained by chemical and enzymatic cleavage.