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There is no readily available technique for measurement of liver oxygenation and function. Near infrared spectroscopy (NIRS) is a non-invasive technique originally developed for measuring cerebral oxygenation. This thesis has investigated its application for measurement of changes in hepatic tissue oxygenation and function. A new algorithm was developed for the hepatic application of NIRS. It was validated by comparing tissue oxygenation changes measured by NIRS with hepatic vein oxygenation in pigs. A significant correlation was found between hepatic vein oxygen partial pressure and hepatic oxyhaemoglobin (HbO2), deoxyhaemoglobin (Hb), and cytochrome oxidase (Cyt Ox) (r = 0.87, -0.86, and 0.91, respectively). NIRS measurement of Cyt Ox changes as an indicator of the intracellular tissue oxygenation correlated (r= 0.91) with cellular adenosine triphosphate levels measured by magnetic resonance spectroscopy. A possible role for NIRS in monitoring hepatic blood flow was investigated in pigs by correlating liver tissue oxygenation and blood volume measured by NIRS with hepatic artery and portal vein blood flow. Changes to liver blood inflow were immediately reflected by alterations in liver tissue oxygenation and blood volume. With hepatic artery occlusion there was a significant decrease in Hb02 and total haemoglobin (HbT). Portal vein occlusion caused a greater reduction in Hb02 and HbT with a significant decrease in Cyt Ox. Total occlusion caused a further a decrease in Hb02 and HbT with a significant decrease in Cyt Ox. To investigate the possible role of NIRS in evaluating liver dysfunction, a rabbit model of ischaemia reperfusion (I/R) injury was used. Changes in hepatic Hb02 correlated with reduced flow in the hepatic microcirculation (HM) (r = 0.94). HbO2 changes correlated with the hepatocellular injury as shown by serum ALT, AST, and LDH (r = 0.89, 0.81 and 0.77, respectively). Also, HbO2 changes correlated with the reduction in the bile volume (r = -0.91). Intracellular oxygenation as reflected by changes of Cyt Ox correlated with HM changes (r = 0.93). A significant correlation was found between the Cyt Ox and serum ALT, AST, and LDH (r = 0.97, 0.90, and 0.85, respectively). Also, Cyt Ox correlated significantly with bile volume (r = -0.93). NIRS can measure hepatic indocyanine green (ICG) and this was studied in different animals models. In a rabbit model of acute hepatic dysfunction, ICG uptake rate correlated significantly with total hepatic blood flow (THBF) and HM (r = 0.79 and 0.59, respectively). In a rabbit l/R model, ICG excretion rate correlated with serum ALT, AST, and LDH (r = -0.73, -0.61, and -0.56, respectively) and bile volume (r = 0.83). In a rabbit model of fatty liver ICG rate of uptake correlated with THBF (r = 0.94) and HM (r = 0.96) and its excretion rate correlated with serum bilirubin (r = -0.89), ALT (r = -0.87), AST (r = -0.90), and albumin (r = 0.95). In conclusion NIRS can be used to monitor changes in hepatic tissue oxygenation and function. This technique has potential for clinical application in liver surgery and transplantation for evaluating hepatic tissue viability.