Once inside liver parenchymal cells, all-trans-retinyl esters (atREs), are hydrolysed to all-trans-retinol (atROL) and fatty acids (FAs) by a neutral, all-trans-retinyl ester hydrolase (NREH). No NREH has been characterised yet although both acidic and neutral REH activity has been shown to be associated with endosomes and plasma membrane preparations from rodent livers (Harrison & Gad 1989, Gad & Harrison 1991, Hagen et al. 1999). As the acidity increases, early endosomes change to late endosomes and further hydrolysis of atREs is mediated by acid retinyl ester hydrolase (AREH). Like NREH, AREH has not yet been characterised (see refs above). The translocation mechanism of atROL to cytosol is unknown.