Events leading to hyperactivity of human blood platelets are accompanied by an enhanced risk of atherosclerosis and arterial thrombosis. Lipoprotein disorders affect platelet functions, and hypersensitive platelets are observed in various stages of hyperlipidemia. Low-density lipoprotein (LDL), a circulating complex of lipids and proteins that is increased in hypercholesterolemia, enhances platelet function and increases sensitivity of platelets to several naturally occurring agonists. LDL sensitizes platelets via binding of apoB-100 to a receptor on the platelet membrane and via transfer of lipids to the platelet membrane. The receptor that mediates binding of LDL to the platelet and initiates subsequent intracellular signaling cascades has not yet been identified. Modification of native LDL generates a platelet-activating particle, and this interaction might contribute to the development of the atherosclerotic plaque. Lysophosphatidic acid is formed upon mild oxidation of LDL and is responsible for subsequent platelet activation induced by the modified LDL particle. Thus, LDL changes the functions of platelets via a broad spectrum of interactions.