METHODS Tissue oxygenation, measured in peripheral tissue as transcutaneous PO2 (PtCO2) and subcutaneous PO2, was compared with the oxygenation in GI mucosa, which was measured as intramucosal wall pH (pHi), during experimental hemorrhagic shock and resuscitation in pigs. The pigs were hemorrhaged stepwise to a BP of 80 and 45 mm Hg, followed by retransfusion. PtCO2 was measured in the groin and subcutaneous PO2 was measured in the hip region. Intraluminal PCO2 was measured in the stomach, in the small intestine, and the sigmoid colon using silicone catheters. A simultaneous determination of arterial blood HCO3 concentration allowed pHi to be calculated using Henderson-Hasselbalch equation. Cardiac output was determined by thermodilution, and oxygen delivery (DO2) was calculated. RESULTS Early indications of shock were decreases in PtCO2 and intestinal pHi (p less than .01). All measured variables decreased at the second step of bleeding. PtCO2 and subcutaneous PO2 was correlated to DO2 through the entire experiment (r2 = .25 and .49, respectively). Also, the pHi of the small intestine and the sigmoid colon correlated with DO2 (r2 = .36 and .25, respectively). PtCO2 and subcutaneous PO2 correlated with pHi in the small intestine and sigmoid colon. CONCLUSIONS PtCO2 and pHi in the small intestine and sigmoid colon were the variables that most rapidly indicated blood volume loss. Subcutaneous PO2 and PtCO2, and small intestine and sigmoid colon pHi were correlated to total body oxygen transport. Peripheral tissue perfusion followed intestinal perfusion to some extent.