Controversy exists as to the best means to monitor the critically ill patient and the appropriate end points of therapy. Use of global hemodynamic or metabolic parameters may be normal in the patient who has not been completely or adequately resuscitated. Decreased perfusion to the gut is not well tolerated and may contribute to the development of the multiple organ dysfunction syndrome. Gastric tonometry is a minimally invasive way to monitor splanchnic perfusion in the critically ill patient. Data suggest that tonometry is useful for outcome prognostication and for detection of early hypovolemia. In addition, use of gastric intramucosal pH or mucosal-arterial CO(2) gap as end points of resuscitation may be superior to other conventional whole-body parameters. For these reasons, gastric tonometry must be considered the hemodynamic monitor of choice.