Although ATP-MgCl2 produces a myriad of beneficial effects following organ ischemia and simple hemorrhagic shock in animal models which involved heparinization and/or blood resuscitation, it is not known whether ATP-MgCl2 has any salutary effect on the depressed active hepatocellular function (AHF) and hepatic microvascular blood flow (HMBF) in a nonheparinized model of trauma and severe hemorrhage in the absence of blood resuscitation. To determine this, rats underwent a midline laparotomy (i.e., trauma induced) and were bled to and maintained at a mean arterial pressure of 40 mm Hg until 40% of the maximum shed blood volume was returned in the form of Ringer's lactate (RL). The animals were then resuscitated with four times the volume of shed blood with RL. ATP-MgCl2, 50 μmoles/kg body weight (BW) each or an equivalent volume of normal saline, was infused intravenously for 95 min during and following crystalloid resuscitation. At 1.5 and 4 hr after resuscitation, AHF (Vmax, maximal velocity of indocyanine green clearance; Km, efficiency of the active transport process) was determined without blood sampling by using an in vivo indocyanine green clearance technique. HMBF was measured with laser Doppler flowmetry. Results indicate that Vmax, Km, and HMBF decreased significantly at 1.5-4 hr after hemorrhage and resuscitation. ATP-MgCl2 infusion restored the depressed Vmax, Km, and HMBF and prevented the occurrence of hepatic edema. The restoration of AHF with ATP-MgCl2 treatment may be due to its direct salutary effect on the active indocyanine green transport process and/or due to improvement in hepatic microcirculation. Thus, ATP-MgCl2 appears to be a promising adjunct to the treatment of hepatocellular dysfunction following trauma and severe hemorrhagic shock even in the absence of blood resuscitation. © 1991.