Coronary heart disease (CHD) is the leading cause of death in America. CHD is multifactorial, and low plasma high-density lipoprotein cholesterol (HDL-C) levels are among the most common biochemical abnormalities observed in CHD patients. The mechanisms controlling plasma HDL-C levels are poorly understood. However, several groups recently reported that mutations at the ATP-binding cassette transporter 1 gene (ABC1) are responsible for a rare disorder known as Tangier disease, which is characterized in the homozygous state by the virtual absence of circulating plasma HDL. This new finding represents a major breakthrough in our knowledge of lipoprotein metabolism and, more specifically, the reverse cholesterol transport. This information could lead to a more precise assessment of the genetic predisposition to CHD as well as to new therapeutic tools to prevent and treat CHD.