Arachidonic acid (ARA) is one of the most abundant polyunsaturated fatty acids (PUFAs) in the mammalian brain. Many enzymatically- and nonenzymatically-produced metabolic products have important and potent pharmacological properties. However, uniformly isotope labeled forms of ARA are not commercially available for studying the metabolic fates of ARA. This study describes a simple and efficient protocol for the biosynthesis of U-C-13-ARA from U-C-13-glucose, and U-C-14-ARA from U-C-14-glucose by Mortierella alpina. The protocols yield approximately 100 nmol quantities of U-C-13-ARA with an isotopic purity of 95% from a 500 mu l batch volume, and approximately 2 mu Ci quantities of U-C-14-ARA with an apparent specific activity in excess of 1200 Ci/mol from a 250 mu l batch volume. (C) 2016 Elsevier Ltd. All rights reserved.