From the standpoint of boiler-wall corrosion prevention, preliminary studies indicated that a chelating agent, ethylenedinitrilotetraacetic acid (H4EDTA), in conjunction with lithium hydroxide is preferable to the low- phosphate control treatment presently being used by the Navy. To elucidate the corrosion-inhibition mechanism in the lithium hydroxide-EDTA(4-) system, we must know the rate and the mechanism of EDTA(4-) decomposition in aqueous solutions under conditions of high-pressure boiler operations. As a background for investigations at this Laboratory of the solid phase and solution phase decomposition of EDTA(4-) at high temperatures, the available literature has been examined and pertinent facts related to the lithium hydroxide-EDTA(4-) system are reported. The general properties of EDTA(4-) chelates are reviewed first. Although a considerable amount of information is available related to the use of alkali-metal hydroxides and EDTA(4-) solutions for hard-scale removal and corrosion prevention, no studies have been reported on decomposition products from aqueous EDTA(4-) solutions heated under pressure to high temperatures. The qualitative investigations of the thermal decomposition of solid H4EDTA and its metal salts fail to fully identify the volatile products and residues formed at temperatures near those of boiler operations.