The thermal decomposition of the hydrochloride salts of 2-(4-aminophenyl)- and 2-(2,4-diaminophenyl)malonic acids, the corresponding diethyl esters, and the respective sodium carboxylates has been examined using thermogravimetry. Thermal decomposition of the hydrochlorides of the carboxylic acids occurs by sequential loss of two moles of carbon dioxide per mole of salt followed by loss of hydrogen chloride at approximately 400 degrees C. The corresponding diethyl esters undergo initial degradation by loss of two moles of ethylene and a mole of carbon dioxide per mole of salt. This is followed, in sequence, by loss of a second mole of carbon dioxide and then one or two moles of hydrogen chloride depending on the identity of the amine salt undergoing decomposition. The sodium salts of the neutralized amino acids do not undergo significant decomposition below 800 degrees C.