This 3-hydroxyoctadecanoic acid is a high purity standard that is ideal for analysis and biological systems. 3- Hydroxyoctadecanoic acid is found in many plants and animals as well as in bacteria and other organisms. 3-Hydroxy fatty acids are intermediates in fatty acid biosynthesis and have been found to be converted to the -fatty acid by the enzyme CYP4F11 and then into dicarboxylic acids in vivo.1 3-Hydroxy fatty acids are used as biomarkers for fatty acid oxidative disorders of both the long- and short-chain 3-hydroxy-acyl-CoA dehydrogenases.2,3 Polyhydroxyalkenoates, polyesters produced by bacteria fermentation, are used for carbon and energy storage and are of interest in studies regarding their synthesis, properties and mechanisms. Medium chain-length polyhydroxyalkenoate monomers such as 3- hydroxyoctadecanoic acid may have pharmaceutical properties.