A key goal of biomedical investigators interested in HDL is to establish the relationships between the structure and function of the lipoprotein. The HDL Quantitation Core will provide the powerful tools of mass spectrometry and quantification of HDL particle size and concentration to PPG investigators. Core personnel have documented expertise in these areas, and their capabilities will support PPG investigators with a standardized, validated set of common assays. Core C will also optimize efficiency and cost-effectiveness by providing these services in a central laboratory.