Fatty acyl coenzyme A (CoA) synthetases are a group of enzymes responsible for the activation of fatty acids through ligated high-energy CoA thioester bonds. Ultimately these fatty acyl-CoA conjugates are routed toward either anabolic or catabolic pathways. Long-chain-fatty-acid-CoA ligase 5 (LACS 5) utilizes a wide range of saturated fatty acids with a substrate preference for C16-C18 unsaturated fatty acids. This enzyme represents a new class of potential drug targets, and, hence, our efforts were focused upon developing a robust assay for utilization in a high throughput screen. Toward that end, we describe a radiometric homogeneous measurement of the enzymatic reaction by employing ionic capture of the reaction product onto YSi scintillation proximity assay (SPA) beads. We present kinetic and inhibition data for LACS 5 using this SPA format. Our results show that the assay method is both robust and well suited for this class of lipid-metabolizing enzymes.