Kidney slices from thyroidectomized rats incubated in Ringcr-amino acid media synthesized considerable amounts of glucose, especially from L-prolinc. With added thyroxinc the amount of glucose found slightly exceeded that of the controls when incubated at 37°. When slices were incubated at 5 and 37° the amount of glucose found in the thyroxine vessels greatly exceeded that of the controls. Similar differences existed in the oxygen consumption values. Thyroxine appeared to protect enzyme systems involved in oxygen consumption as well as gluconeogenesis from deterioration at 5°. Thyroxine effects, although noted at 37°, were always associated with an otherwise mctaboli-oally failing system.