The presence of hepatic dysfunction significantly affects the length of hospital stay and the outcome in critically ill patients. Considering the important partial hepatic functions of metabolism, synthesis, detoxification, and excretion, the worse clinical course of patients suffering from hepatic dysfunction is not surprising. The most often used indicator of hepatic dysfunction is bilirubin. However, bilirubin and other commonly used static laboratory tests provide only indirect measures of hepatic function. In contrast to these static tests, dynamic liver tests, such as indocyanine green (ICG) disappearance rate should provide better direct measures of the actual functional state of the liver at the time of assessment. The ICG is a water-soluble inert compound that is injected intravenously. It mainly binds to albumin in the plasma. ICG is then selectively taken up by hepatocytes, independent of adenosine triphosphate (ATP), and later excreted unchanged into the bile via an ATP-dependent transport system. The ICG is not metabolized; it does not undergo enterohepatic recirculation. Thus, ICG excretion rate in bile reflects the hepatic excretory function and hepatic energy status. Because of these features, ICG has been found to be useful to assess liver function in liver donors and transplant recipients, in patients with chronic liver failure, and as a prognostic factor in critically ill patients. Further trials concerning liver dysfunction have applied the noninvasive bedside assessment of ICG among other clinical variables to monitor the progress and/or the reversal of liver dysfunction.