The symptom complex of hematuria, abdominal pain, and nitrogen retention as a manifestation of sulfapyridine therapy was first described by Southworth and Cooke,1although the occurrence of hematuria had been previously noted.2 Animal experiments by Antopol and Robinson,3Gross, Cooper and Lewis4and Toomey5early revealed the pathologic changes in the urinary tract of rats, rabbits and monkeys receiving sulfapyridine. Since then, Antopol and Robinson6and Toomey, Reichle and Takacs7have studied these changes in great detail. Briefly they are as follows: in the kidneys, striking dilatation of the glomerular spaces and tubules; thickening of the basement membranes of the glomerular tufts with changes in the shape of the cells of the capsular epithelium; in the collecting tubules, débris and spaces, apparently the lodging place of crystals of the precipitated drug; in the pelves and ureters, concretions, with denuding of the epithelium, clotted