Recent recognition of the importance of HDL’cholesterol as a stronginverseriskfactorforcoronaryartery disease (1-4) has led to substantial demand for this assay by clinical and research laboratories. Various methods, including ultracentrifugation, electrophoresis, and specific precipitation, have been used to separate the lipoproteins. Although ultracentrifugation techniques are useful for reference (5), they are expensive and require equipment and a level of technical so-phistication not available in many routine laboratories. The precipitation methods have, in general, been most suitable for routine quantitation of lipoproteins. Several such methods have been described in the recent literature, most of them based on earlier work of Burstein et al.(reviewed in 6). The method used most extensively in major population studies involves useof heparin in conjunction with MnS+ to precipitate VLDL and LDL (7-9). HDL is then quantitated in terms of the amount of cholesterol remaining in the supernatant solution. This method has been extensively studied (10, 11) and modifications have been described (11, 12). The procedure has its drawbacks, of which the major one is the reported interference of the Mn2+ with the enzymic assays for cholesterol (13). Also, heparin is relatively expensive and may vary

1 Nonstandard abbreviations: HDL, LDL, VLDL, high-, low-, and very-low-density lipoproteins, respectively; apoA-I, apolipoprotein AI, the major protein of HDL; apoB, apolipoprotein B, the major protein of LDL and VLDL; EDTA, disodium ethylenediaminetetraacetate; CDC, Centers for Disease Control; PIPES, 1, 4-piperazinediethanesulfonic acid; LRC, Lipid Research Clinics.