To determine the relationship of the arterial base deficit (BD) to physiologic indicators of shock and resuscitation--heart rate, mean arterial pressure (MAP), cardiac output (CO), arteriovenous oxygen difference (AVO2), mixed venous oxygen saturation (VSAT) and oxygen delivery to consumption ratio (RATIO)--16 swine were monitored invasively, bled 40 per cent of their calculated blood volume and resuscitated with crystalloid and blood. During hemorrhage, the MAP, CO, VSAT and RATIO decreased and the BD and AVO2 increased. One hour after hemorrhage, but before crystalloid infusion, the MAP, VSAT and RATIO had increased significantly from previous levels and the AVO2 had narrowed significantly, while the BD showed no significant change. All parameters returned to baseline with resuscitation. BD accurately reflected the hemodynamic and tissue perfusion changes associated with hemorrhagic shock and resuscitation in this model. BD can be used as an indicator of the severity of the shock state and the efficacy of resuscitation when invasive monitoring is impractical or not available. BD was more reflective of the true volume deficit during compensated shock than other physiologic variables in this study.