Lipoprotein(a) (Lp[a]) represents a class of plasma lipoprotein particles that have overall characteristics similar to low-density lipoproteins but distinct from them by having apolipoprotein B100 linked to apolipoprotein(a) by disulfide bridge(s). This protein has recently been shown to have a striking amino acid sequence homology with plasminogen, a serine protease zymogen that on activation to plasmin promotes the conversion of fibrinogen to fibrin. The high incidence of Lp(a) in the plasma of patients with cardiovascular disease has been noted by many investigators. The new knowledge being rapidly acquired on the structure of Lp(a) should facilitate the understanding of the mechanism of its atherogenicity and perhaps shed light on its possible physiologic role.