Chemical changes induced in Palo Duro and Paradox Basin natural rock salts and in synthetic NaCl by heat and gamma radiation were investigated. Heating of unirradiated natural rock salts to 300 degree C resulted in HCl (most prevalent), SO//2, CO//2, and H//2S evolution, and increased the base content of the remaining salt by not more than 10 microequivalents per gram; whereas, heating of synthetic NaCl gave no product. Gamma irradiation produced sodium colloids and neutral chlorine in amounts similar to the results of Levy and coworkers. Radiation and heat introduced by high-level nuclear waste package emplacement in a repository in salt will induce physical and chemical changes in the salt. These changes can alter the near-field chemical environment of the waste package and thus may influence the durability of waste package materials.