This enzyme, abundant in the retinal pigment epithelium, catalyses the reduction of 11-cis-retinol to 11-cis-retinal [1] while the substrate is bound to the retinal-binding protein [4]. This is a crucial step in the regeneration of 11-cis-retinal, the chromophore of rhodopsin. The enzyme can also accept other cis forms of retinol [2].