Seven patients with acute renal failure due to gross haematuria caused by glomerulonephritis are described. Gross haematuria lasting 4-40 days led to acute impairment of renal function of variable severity (peak plasma creatinine 1.3-12 mg/dl) and duration. While partial recovery of renal function occurred in all patients within few days, complete remission was observed only some months later. Three patients had IgA nephropathy (2 the primary form and 1 nephritis secondary to Schönlein-Henoch purpura), two patients had acute postinfectious glomerulonephritis, and two others had focal necrotizing (pauci-immune) glomerulonephritis. The glomerular changes seen in the renal biopsy were not enough to explain per se the renal function impairment. Tubular changes, however, were severe and consisted of tubular necrosis, erythrocyte casts, erythrocyte phagocytosis by tubular cells, accompanied by interstitial damage (oedema, red-cell extravasation, and inflammatory infiltrates). Study of the renal biopsies by immunofluorescence revealed no retrodiffusion of Tamm-Horsfall protein into the glomerular Bowman's space, a sign of obstructed tubular flow in any case. It is concluded that acute renal failure due to gross haematuria in glomerulonephritic patients may not occur only in IgA nephropathy, as reported so far, and is not associated with intratubular obstruction.