Empirical Formula (Hill Notation): C26H24N4O, Molecular Weight: 408.49, certified by the Biological Stain Commission, Synonym: 1-([4-(Xylylazo)xylyl]azo)-2-naphthol, 1-[2,5-Dimethyl-4-(2,5-dimethylphenylazo)phenylazo]-2-naphthol, Solvent Red 27. Oil Red O is a lysochrome. It is used to stain and visualise general localization of fats.