Storage of donor livers in Euro-Collins solution for human transplantation surgery is limited to about 8 hr. Here, tissue damage to isolated rat livers stored under the same conditions as human livers was characterized following reperfusion. The purpose of this work was to determine the importance of nutritional status on injury due to cold storage and reperfusion, to establish whether lethal injury occurs during cold storage or only after reperfusion, and to identify the cell types most vulnerable to damage. Rat livers were perfused with Krebs-Henseleit-bicarbonate buffer, stored 8 to 48 hr in Euro-Collins solution and reperfused with warm, oxygenated Krebs-Henseleit buffer for 15 min. Nuclear trypan blue uptake and lactate dehydrogenase release were used as indices of cell death. After 8 hr of cold storage and reperfusion, little loss of parenchymal or nonparenchymal viability occurred. After 24 or 48 hr, virtually all parenchymal cells remained viable. However, severe damage to nonparenchymal cells was observed, and about 40% of nonparenchymal cells were trypan blue positive. Nutritional status (fed vs. fasted) did not affect the extent of cell damage. Nonparenchyma cell killing was accompanied by cellular rounding, nuclear pyknosis and protrusion of cells into sinusoidal lumens. Scanning electron micrographs demonstrated denudation of the sinusoidal lining. Rounding and pyknosis were not observed in 24-hr-stored livers which were not reperfused, and trypan blue uptake did not occur in stored livers infused with cold, anoxic Euro-Collins solution. Based on cytochemistry and electron microscopy, lethal cell injury occurred predominantly to endothelial cells. Storage of livers in University of Wisconsin cold storage solution, which has been shown to extend preservation of livers for transplantation surgery, protected endothelial cells from reperfusion injury after cold ischemic storage. The data suggest that damage to stored livers leading to graft failure after transplantation involves a reperfusion injury to hepatic endothelial cells. Identification of this injury in isolated livers by trypan blue labeling provides a rapid and inexpensive means to evaluate and improve liver preservation solutions.