The adequacy of perfusion of the gut and liver is likely of major importance in critically ill patients because inadequate perfusion could be associated with hepatic and gut injury and dysfunction and consequently patient morbidity and mortality. This article summarizes the various invasive and noninvasive techniques for directly and indirectly assessing the adequacy of splanchnic blood flow and its response to therapeutic interventions. These techniques may yield prognostically important variables and contribute to therapeutic decisions made in various conditions, thereby supplementing global monitoring techniques applied in critically ill patients. Nevertheless, many of these assessments are not applicable on a routine basis because of either their invasive nature or interpretational difficulties. Future studies may be necessary to further define the role of monitoring the adequacy of splanchnic perfusion in the critically ill.