The measurement of lipoprotein (a) [henceforth abbreviated as Lp(a)] is of growing clinical interest because of its potential use as a strong and independent predictor for the development of coronary and cerebrovascular diseases. This association and the possible role of Lp(a) in thrombogenesis have greatly stimulated population-based studies and basic research into the genetics, structure, function, metabolism, and disease association of Lp(a). These studies have created a demand for the rapid development of commercially available immunoassays for the measurement of Lp(a) in human plasma. However, many problems have been identified with the immunochemical measurement of Lp(a) due to the complexity and heterogeneity of the protein structure of Lp(a) and the homology of apo(a) with plasminogen. There has been inadequate standardization of the various Lp(a) assays and there are no generally accepted reference materials and methods. Also, there is no consensus on how to express plasma Lp(a) values; some assays express Lp(a) as total lipoprotein mass, whereas others use total protein mass. Often there is no reference to population-based reference values. Additionally, none of the existing assays have been evaluated to establish what exactly is being measured, i.e., Lp(a), free apo(a), or apo(a) associated with triglyceride-rich lipoproteins. In addition, it has not been determined whether the antibodies employed in the assays are equally immunoreactive with all the various forms of apo(a). This contract if for the development of commercially available immunoassays for the measurement of Lp(a) in human plasma.