Deuterated homo-and heterocyclic aromatic substrates bearing various functionalities were prepared by isotope exchange in supercritical deuterium oxide, with little or no formation of byproducts. Equilibration was attained rapidly (1–24 hrs), and deuterium exchange extended to alpha positions of alkyl homologs. Nitro-and haloarenes, thioethers, telluroethers, and some heterocyclic substrates were unstable.