—Plasma high density lipoprotein (HDL) levels show an inverse relationship to atherogenesis, in part reflecting the role of HDL in mediating reverse cholesterol transport. The transfer of HDL cholesterol to the liver involves 3 catabolic pathways: the indirect, cholesteryl ester transfer protein (CETP)–mediated pathway, the selective uptake (scavenger receptor BI) pathway, and a particulate HDL uptake pathway. The functions of the lipid transfer proteins (CETP and phospholipid transfer protein) in HDL metabolism have been elucidated by genetic approaches in humans and mice. Human CETP deficiency is associated with increased HDL levels but appears to increase coronary artery disease risk. Phospholipid transfer protein deficiency, produced by gene knockout in mice, results in decreased HDL levels, reflecting decreased transfer of phospholipids from triglyceride-rich lipoproteins into HDL. Obese (ob/ob) mice have markedly increased HDL levels and represent an interesting model of defective HDL catabolism in the liver. In hepatocytes of wild-type mice, there is extensive uptake and resecretion of HDL and selective uptake of cholesteryl ester from HDL during recycling. In ob/ob mice, these processes are defective, suggesting that HDL recycling plays an important role in holo-HDL catabolism, selective uptake, and the determination of plasma HDL levels.