A low fractional excretion of sodium (FENa) of less than 1% was present in two patients who had acute renal failure due to sepsis. Both patients had bacteremia and had undergone major abdominal and vascular surgery. Prerenal azotemia due to volume depletion was not present as adequate central filling pressures were maintained with a Swan-Ganz catheter. Interstitial nephritis and obstructive uropathy were carefully ruled out. Acute renal failure due to sepsis should be included among the other conditions recently reported with a low FENa. This is of great importance as errors in fluid management are possible in this high-risk patient population when much reliance is placed on the interpretation of a low FENa of less than 1%.