Background. Despite aggressive intensive medical management acute liver failure (ALF) may require high-urgency liver transplantation (LTx). Available prognostic scores do not apply for all patients; reliable tools to identify individuals in need of LTx are highly required. The liver maximum function capacity test (LiMAx) might represent an appropriate option. Referring to a case of ALF after Amanita phalloides-intoxication the potential of the LiMAx-test in this setting is discussed. Presentation of Case. LiMAx was performed in a 27-year-old patient prior to and after high-urgency LTx. In accordance with clinical appearance of hepatic encephalopathy, coagulopathy, and acute kidney failure, the LiMAx-test constituted a fulminant course of ALF with hardly any detectable metabolic activity. Following LTx with a marginal donor organ (95% hepatosteatosis), uptake of liver function was demonstrated by postoperative increase of the LiMAx-value. The patient was discharged from hospital on postoperative day 26. Discussion. ALF often is associated with a critical state of the patient that requires almost immediate decision-making regarding further therapy. Application of a noninvasive liver function test might help to determine the prognosis of ALF and support decision-making for or against LTx as well as acceptance of a critical donor organ in case of a critically ill patient.