Although ATP-MgCl2 enhances the recovery of renal function after ischemia and reperfusion, it is not known whether this agent has any beneficial effects on renal microcirculation and function in a nonheparinized model of trauma and severe hemorrhage. To study this, a midline laparotomy was performed (i.e., trauma induced) and the rats were bled to and maintained at a mean arterial pressure of 40 mmHg (1 mmHg = 133.32 Pa) until 40% of the maximum shed blood volume was remrned in the form of Ringer's lactate (RL) solution. Animals were then resuscitated with 4 times the volume of the shed blood in the form of RL. ATP-MgCl2, 50 μmol/kg body weight, or an equivalent volume of saline, was infused intravenously during and following resuscitation. Renal microcirculation was examined by using colloidal carbon infusion and laser Doppler flowmetry. Glomerular filtration rate (GFR) was assessed with [3H]inulin clearance and cardiac output (CO) was determined by dye dilution technique. The results indicate that the depressed renal microcirculation following hemorrhage and resuscitation was restored by ATP-MgCl2 treatment. GFR was significantly higher in ATP-MgCl2-treated than saline-treated rats. ATP-MgCl2 also increased urine output, restored the decreased CO, and prevented the occurrence of renal edema after hemorrhage and resuscitation. Thus, ATP-MgCl2 appears to be a useful adjunct to crystalloid resuscitation following trauma and severe hemorrhagic shock even in the absence of blood resuscitation.