The purpose of this study is to demonstrate renal injuries by gold sodium thiomalate (G) with ultrastructual changes and gold deposition in kidney tissue using X-ray energy dispersive analysis (XEDA). Twenty-five mg of G containing 12.1 mg of Au was injected into rats intraperitoneally. The rats were divided into 5 groups. Group 1 was sacrificed 6 hours after the injection of G, and group 2 after 24 hours, group 3 after 72 hours and group 4 after 144 hours. Group 5 consisted of the control-rats which were provided with injections of saline. Gold contents in kidneys, liver, lungs and spleen were measured using the flameless atomic absorption method. XEDA was also performed in order to confirm the gold deposition in tissue. Among the organs, only the kidney showed remarkable changes with increased weight. Group 1 already showed marked azotemia which reached to the maximum level in group 3. The amount of gold content in the organs did not change significantly in spite of a marked reduction of serum gold concentration among the 4 groups. Histological examinations revealed marked degeneration and necrosis of pars recta in proximal tubules, although no prominent abnormalities of glomeruli could be observed. Using an electron microscope, many electron dense particles in lysosome were noticed, mainly in proximal tubules. We also found these particles in lysosome of glomerular epithelial cells. Using XEDA, these electron dense particles were demonstrated to be gold, since characteristic energy of gold was found. In conclusion, the kidney was shown to be the most accumulative organ of gold. G caused acute extensive necrosis of proximal tubules. Gold was demonstrated as electron dense particles in lysosomes mainly in proximal tubules, but also partly in glomeruli. Therefore, it was confirmed that a large amount of G had a strong nephrotoxic effect in rats.