Abstract: An improved enzymic assay and assay composition for acetate ion in a biological fluid (e.g., blood serum or tissue extract) or a solution of fruit juice origin (e.g., wine). The acetate ion is reacted with adenosine triphosphate in the presence of enzymic quantities of phosphotransacetylase to form adenosine diphosphate. The above procedure is accelerated by the presence of Coenzyme A and phosphotransacetylase enzyme during the formation of adenosine diphosphate. Thereafter, the quantity of adenosine diphosphate may be assayed by known enzymic techniques. The procedure may be employed for analysis of acetate esters (e.g., ethyl acetate) by hydrolysis to acetate ion in the presence of esterase.