Arylmalonate decarboxylase (EC. 4. 1. 1. 76) catalysed decarboxylation followed by enantioface-differentiating protonation of [alpha-H-2]- and [alpha-H-1]phenylmalonic acid in (H2O)-H-1 and (H2O)-H-2 respectively, gave highly enantiomerically enriched (R)- and (S)-[alpha-H-2]phenylacetic acid in quantitative yields.