AIM: To characterize hyperlactatemia in patients with non-acetaminophen acute liver failure (ALF) in an attempt to clarify the mechanisms implicated and the role as a prognosis factor.METHODS: In the setting of liver transplantation, 63 consecutive patients with non-acetaminophen acute liver failure were studied in relation to tissue oxygenation,hemodynamic and metabolic parameters. Before and after transplantation, the number of infected patients and outcome were registered.RESULTS: Acute ALF showed higher levels of lactate than subacute ALF (5.4±1 mmol/L versus 2.2 ± 0.6 mmol/L, P=0.01). Oxygenation parameters were within the normal range. Lactate levels showed good correlation with respiratory quotient (r= 0.759, P< 0.005), mean glucose administration (r=0.664, P=0.01) and encephalopathy (r=0.698, P= 0.02), but not with splanchnic arteriovenous difference in PCO2, pH and the presence of infection (P=0.1). Portal vein lactate was higher (P< 0.05) than arterial and mixed venous lactate,suggesting its production of hyperlactatemia in the intestine and spleen. The presence of infection was an independent predictor of survival. CONCLUSION: Hyperlactatemia is not a prognosis factor due to byproduct of the overall acceleration in glycolysis.