Lipoprotein (a) is an antigenic variant of low density lipoprotein and is present in the plasma of most people. Many epidemiologic studies from Europe and North America have found that when plasma levels of lipoprotein (a) exceed 0.20 g/L, there is a significantly higher risk of coronary and cerebrovascular atherosclerosis. Until recently, there has been little insight into the function of lipoprotein (a) or its potential atherogenic mechanism. Molecular biological studies have shown that the characteristic protein of lipoprotein (a), called apolipoprotein (a), strongly resembles plasminogen, the precursor of the natural anticoagulant plasmin. Furthermore, there is emerging evidence that lipoprotein (a) is the missing link between the lipoprotein and coagulation systems, acting perhaps as a vehicle which delivers cholesterol to the site of intravascular damage, or as an inhibitor of plasminogen activation at the site of an evolving thrombus.