The objective of this study was to compare the cardiac and hemodynamic responses to a rapid infusion of 1000 ml of modified fluid gelatin (group A) or 1000 ml of lactated Ringer's solution (group B) in emergency room patients suffering from shock. This prospective, randomized, open, noncrossover study was performed at a medical center university hospital in a surgical resuscitation room in the emergency department. The subjects were 34 patients with either hypovolemic or neurogenic shock who were admitted to the emergency room. A resuscitation protocol according to Advanced Trauma Life Support (ATLS) with an additional central venous line or Swan-Ganz catheters for hemodynamic monitoring was used. Physical parameters and hemodynamic variables were measured at baseline and 15 minutes, 30 minutes, and 1 hour after the infusion of each fluid. In both groups the mean arterial blood pressure (MAP), systolic and diastolic pressure, central venous pressure (CVP), and pulmonary artery occlusion pressure (PAOP) increased significantly. The CVP and PAOP increased significantly more in the modified fluid gelatin resuscitation group. In patients with traumatic or neurogenic shock due to acute volume deficiency, there was significantly better hemodynamic improvement, judged by CVP and PAOP measurements using the modified fluid gelatin for volume replacement than with lactated Ringer's solution during the first hour of resuscitation.