A new method has been developed for the separation of (3-¹⁴C) 3-Hydroxy-3-methxlglutaric acid from a (3-¹⁴C) 3-Hydroxy-3-methylglutaryl CoA preparation using Sephadex G^-15 column chromatographv. This method is simple, rapid and is useful in studies where the preparation of (3-¹⁴C) 3-Hydroxy-3-methylglutaryl CoA is required to be free from (3-¹⁴C) 3-hydroxy-3-methylglutaric acid contamination.