OBJECTIVE To determine the value of intramucosal pH for evaluating the effectiveness of treatment for hemorrhagic shock. METHODS Randomized, controlled trial. METHODS University center, animal laboratory. METHODS Eighteen piglets, weighing 17 to 23 kg. METHODS Anesthetized animals were bled to a mean arterial pressure (MAP) of 40 to 50 mm Hg and a 70% reduction in cardiac output during a 1-hr period. This state was maintained for the next hour. The piglets were treated with crystalloid solution to restore cardiac output and MAP during the subsequent 80 mins of the experiment. Some animals were given vasoactive drugs during volume therapy to modulate splanchnic perfusion and increase the diversity of values of various variables. RESULTS Systemic hemodynamic and oxygen transport variables were monitored. Tissue oxygen tensions were measured in the liver and abdominal subcutaneous tissue layer. Gut intramucosal pH (pHi) was determined, using a balloon tonometer. The animals were divided into responders (n=9) and nonresponders (n=9) according to whether pHi increased or decreased during resuscitation. Hemodynamic and oxygen transport variables improved in the group of responders. In the group of nonresponders, values decreased. Liver and subcutaneous oxygen tensions increased during the initial phase of resuscitation in both groups but decreased after 30 mins in the nonresponder group. CONCLUSIONS The change in pHi during the first hour of resuscitation could be used to divide animals treated uniformly from a hemodynamic point of view into two distinct groups with seemingly different outcome. The minimally invasive method could be of value for early evaluation of the results of treatment of hemorrhagic shock.