A novel assay has been developed for the detection of ( R)-phenylacetylcarbinol, ( R)-PAC, a chiral intermediate in the industrial synthesis of ephedrine. It is the product of a biotransformation of benzaldehyde catalysed by the enzyme pyruvate decarboxylase. The assay, using 2,3,5-triphenyltetrazolium chloride, enables high-throughput photometric analysis of the activity of the enzyme thus avoiding time-consuming chromatographic procedures.