During resuscitation of the patient suffering from hemorrhagic shock, it may be difficult to determine the adequacy of treatment in the acute setting. The objective of these preliminary studies was to determine if monitoring perfusion of the gastrointestinal tract as estimated by gastric intramucosal pH (pHi) is useful as a guide during the treatment of hemorrhagic shock. Dogs were bled using a modified Wigger's method to a mean arterial blood pressure of 50 mmHg, and pHi was determined 30, 60, 90, and 120 min later. Gastric intramucosal acidosis developed within 30 min of induction of hemorrhagic shock. It was also found that pHi decreases with relatively small amounts of blood loss. There was a significant fall in pHi following hemorrhage to a mean arterial pressure of 80 mmHg from a baseline pressure of 100 mmHg. Following the reinfusion of shed blood, the pHi returned to baseline values within 30 min. It is concluded that measurements of pHi may be a useful monitor in the evaluation and initial resuscitation of patients in hemorrhagic shock.