27-hydroxycholesterol is transported from the mitochondrial matrix to the extracellular space. In humans, this event is the major source of 27-hydroxycholesterol in the blood and is the means by which the molecule, generated from cholesterol in a variety of cell types, notably macrophages, is transported to the liver for conversion to bile acids and bile salts (Babiker et al. 1999; Bjorkhem et al. 1994). While transport proteins are likely to play a role in this process, the relevant proteins have not been identified.