Apolipoprotein(a), apo(a), the distinctive glycoprotein constituent of lipoprotein(a), Lp(a), is synthesized in the liver, links covalently to apoB100-lipoprotein, and travels so linked in the plasma to tissue sites where removal mechanisms are yet undetermined. Depending on the redox status of the surrounding milieu, apo(a) may re-acquire its unbound state shown to have structural and functional properties different from those of the bound form. Apo(a) is potentially athero-thrombogenic, a property which may be influenced by its size, sequence polymorphism, type of lipoprotein it is linked to and the inflammatory state of the vessel wall. This set of variables must be taken into account when assessing the cardiovascular pathogenicity of free and bound apo(a).