AbstractAn enzymatic synthesis of [11C]N‐acetyl‐D‐glucosamine is described.11CO2is reacted with methylmagnesium bromide to form [1‐11C]acetate. The latter is converted to [11C]acetylcoenzyme A by passage over an enzyme reactor containing immobilized acetylcoenzyme A synthetase (Acetate: CoA ligase (AMP forming); EC 6.2.1.1).[11C]Acetylcoenzyme A is purified on‐line and concentrated on an anionexchange column. Elution is achieved with 1.5 M glucosamine HCl pH 8.0 and the [11C]acetylcoenzyme A fraction is collected in an ultrafiltration cell containing the enzyme glucosamineN‐acetyltransferase (acetylcoenzyme A: 2‐amino‐2‐deoxy‐D‐glucoseN‐acetyl