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.