Apolipoprotein A I promotes cholesterol efflux from tissues to the liver for excretion. Apolipoprotein A I is the major protein component of high density lipoprotein (HDL) in the plasma. Synthesized in the liver and small intestine, it consists of two identical chains of 77 amino acids, an 18 amino acid signal peptide is removed co-translationally and a 6 amino acid propeptide is cleaved post-translationally. Apolipoprotein A I is a cofactor for lecithin cholesterolacyltransferase (LCAT) which is responsible for the formation of most plasma cholesteryl esters. Defects in the Apolipoprotein A I gene are associated with HDL deficiency and Tangier disease. The therapeutic potential of apoA-I has been recently assessed in patients with acute coronary syndromes, using a recombinant form of a naturally occurring variant of apoA-I. The availability of recombinant normal apoA-I should facilitate further investigation into the potential usefulness of apoA-I in preventing atherosclerotic vascular diseases.Synonyms: APOA1, Apo-AI, ApoA-I, ApoAI