The mercurial diuretics have been well established as therapeutic agents. Toxic reactions are rare when viewed against the frequency of diuretic therapy. Nephrotoxicity, one of the more serious complications of mercurial diuretics, has been both denied and documented (1). The present study adds 5 cases of renal tubular necrosis due to mercurial diuretics. Histologic material was drawn from the Georgetown University Hospital and Armed Forces Institute of Pathology. Criteria for inclusion were: 1. Acute onset of oliguria, and renal failure following the administration of mercurial diuretic; 2. No other ready explanation for the oliguria; 3. A clinical course consistent with