A 32-year-old man presented with acute renal failure during an influenza epidemic. He had been well until 7 days before admission, when he noted the sudden onset of headache, fatigue, malaise, nausea, and fever. The next day vomiting and diarrhea developed, and 5 days before admission his physician prescribed amoxicillin 500 mg four times daily by mouth. The patient took only six doses, discontinuing the drug due to persistent emesis. Three days before admission, myalgias, arthralgias, and gross hematuria developed. The patient was referred for admission when routine blood chemistry showed a serum creatinine of 1,315 J.lmol/L (15 mgjdL), normal less than 110 J.lmol/L (1.2 mg/dL). One year before, a routine urinalysis had shown hematuria without proteinuria. At that time, an intravenous pyelogram, renal ultrasound, and serum creatinine concentration were normal. Routine blood chemistry 1 month before admission showed a serum creatinine of 118 J.lmol/L (1.3 mg/dL), at which time a urinalysis showed microscopic hematuria and mild proteinuria by dipstick. At the time of admission, physical examination was normal, and, of note, no rash was present. A urinalysis showed gross hematuria, 0.6 gjL of proteinuria by dipstick, and many finely granular, white blood cell, and red blood cell casts were noted on microscopic examination. Admission laboratory data were as follows: serum sodium 132 mmol/L, potassium 3.9 mmol/ L, chloride 89 mmol/L, and bicarbonate 20.1 mmol/L. The hemoglobin was 92 gjL, white blood cell count 14.9· 109/L, of which 65% were granulocytes, and 27% were lymphocytes. No eosinophilia was remarked in the smear, and the platelet count was 447 . 109/L. Immunologic studies showed a negative anti-DNA titer, with normal levels of complement and immunoglobulins. Hepatitis antigen screening was negative. Indirect immunofluorescence for antiglomerular basement membrane and antineutrophil cytoplasmic antibodies were negative. Cultures of blood and throat were negative, and the anti-streptolysin 0 titre was 12 Todd units. Acute and con-