Patients admitted to study sites with carefully defined criteria for acute liver failure and who are thought not to have acetaminophen toxicity, mushroom poisoning, pregnancy-related liver failure, or malignancy will be eligible. Each patient will receive intravenously in solution of 5% dextrose in water containing N-acetylcysteine, beginning at a dose of 150 mg/kg bodyweight in 250 ml 5% dextrose over one hour, and in declining doses over a total of 72 hours. Care of patients and consideration of transplantation or other clinical decisions will not be affected by the study or the use of study drug.