MATERIALS AND METHODS

The procedure of Lindgren et al. involving preparative and analytic ultracentrifugation is in a sodium chloride-D20-Hz0 system of solvent density equal to

1.24 gm/ml. All three high density lipoproteins were observable in the analytical ultracentrifugation at a density of I. 24 gm/ml. This analytical method allowed the quantitative determination of the sum of the concentrations of the HDL2 plus HDI3, but was unsatisfactory for the complete resolution of the HDLZ from HDL3 so that their individual concentrations could be measured. For this reason an additional ultracentrifugal procedure at a density of 1.125 gm/ml was designed for the separate measure of the concentration of the HDLZ. The detailed description of the preparative and analytical ultracentrifugal procedures including film analysis employed for the determination of the three high density lipoproteins is described by deLalla and Gofman (6).

The clinically healthy subjects for this study were obtained from two sources. Males and females below the age of 30 years were volunteers from the student population of the University of California at Berkeley. All other subjects, above the age of 30 years, were randomly selected from the population under study by the Heart Epidemiology Study Group at Framingham, Massachusetts. All subjects had had a recent complete medical examination. The subjects included in the present study as clinically healthy individuals represented those meeting certain requirements in their medical examination. All individuals included in the study had blood pressures, at examination, below 140 mm Hg systolic and 90 mm Hg diastolic. The following illnesses recorded in the medical history or discovered during examination were sufficient to exclude individuals from this study; diabetes, nephritis, rheumatic fever, rheumatoid arthritis, syphilis, tuberculosis, peptic ulcer, asthma, hepatitis, cardio-