9-cis Retinal is a natural retinoid that is produced by oxidation of 9-cis retinol by cis-retinol dehydrogenase (cRDH). It binds to cellular retinol-binding protein-I (CRBP-I) and CRBP-II (Kds = 8 and 5 nM, respectively) and to cellular retinaldehyde-binding protein (CRALBP; Kd = 53.3 nM). In vitro, 9-cis retinal inhibits differentiation of RCJ C5.18 chondrogenic cells into cartilage (IC50 = 8 nM). In vivo, it rescues cone electroretinogram (ERG) responses in Irbp-/- mice, which lack interphotoreceptor retinoid-binding protein and have diminished cone responses, when administered at a dose of 0.375 mg.