The base deficit (BD), is a potentially useful indicator of volume deficit in trauma patients. To evaluate BD as an index for fluid resuscitation, the records of 209 trauma patients with serial arterial blood gases (ABG's) were reviewed. The patients were grouped according to initial BD: mild, 2 to -5; moderate, -6 to -14; and severe, less than -15. The volume of resuscitative fluid administered, change in BD, mean arterial pressure (MAP), and presence of ongoing hemorrhage were analyzed for differences between the BD groups. The MAP decreased significantly and the volume of fluid required for resuscitation increased with increasing severity of BD group. A BD that increased (became more negative) with resuscitation was associated with ongoing hemorrhage in 65%. The data suggest that the BD is a useful guide to volume replacement in the resuscitation of trauma patients.