To the Editor.
—In a recent article in the Archives (138:1419-1421, 1978), Sigala et al reported RBC casts in the urine of a patient with normal glomerular morphology. Although no hemorrhagic lesions were found in the wedge biopsy specimen examined, they concluded that "pure tubulointerstitial disease can be the proximate cause of RBC cast formation." A prerequisite for RBC cast formation is hematuria of renal origin; slight microscopic hematuria was also present in the patient described (five to eight erythrocytes per high-power field).We want to draw attention to endemic benign nephropathy (EBN), found in Nordic countries,1.2 a disease whose etiology is unknown, but which is probably infectious. In EBN, transient hematuria is found in 10% to 75% of the patients.3 However, RBC casts are not reported. The histopathological findings in percutaneous needle biopsy specimens consist of a focal, sometimes hemorrhagic, interstitial inflammatory reaction and signs of degenerative