Ten patients with myoglobinuric and hemoglobinuric acute renal failure demonstrated low fractional excretion of sodium (FENa) values (less than 1%) during the oliguric phase of their course. Acute renal failure secondary to hemoglobinuria developed in five patients, and five demonstrated acute deterioration with myoglobinuria. The mean serum creatinine level increased from 1.1 mg/dL (range, 0.6 to 1.7 mg/dL) to a maximum of 6.9 mg/dL (range, 2 to 13.1 mg/dL). Although three patients required dialysis, all individuals eventually returned or were returning toward their baseline renal function at discharge. The importance of a low FENa in the setting of myoglobinuric and hemoglobinuric renal failure is reviewed. The findings in this report raise the possibility that a common mechanism may underlie the renal injury in both types of pigment toxicity.