The deuterations of a number of the common amino acids at 400 degrees C and 390 bars in aqueous strong acid are reported. Protium/deuterium exchange is found to be rapid at the a carbon in all examples. Decarboxylation occurred in most cases at a sufficiently rapid rate that the reaction could not be used for deuteration at other sites in most cases. Exchange was accompanied by racemization of the alpha chiral center as was previously observed for reaction in supercritical base. While rapid a deuteration was noted for all the amino acids, slower deuteration of alkyl chains was not observed because of decomposition. Electrophilic substitution of activated aromatic groups, however, was more rapid than decomposition leading to the production of some products deuterated at sites other than the a carbon. Several of the decomposition products are identified and a general scheme for the deuteration and decomposition reactions is suggested.