The main site of injury induced during small bowel preservation is perceived to be the basement membrane and the endothelium of the highly vascularized mucosa, an aspect evaluated here in further detail. The effects of preservation were studied using a specific basement membrane stain (laminin antibody), an endothelial cell stain (factor 8 antibody) and standard histology. In addition, mucosal glutaminase activity reflecting entero-cyte integrity was measured as monitor of the extent of preservation injury. Using a rat model, small bowel grafts were harvested, the vascular bed and bowel lumen were flushed, and the grafts were stored (4°C) for 1, 6, 9, and 12 hr and transplanted into syngeneic hosts. After cold storage prior to transplantation, full-thickness small bowel biopsies were obtained for the various tissue preparations. Histologic evaluation at the end of the preservation period revealed separation of the vil-lous epithelium from the lamina propria that increased with extending preservation time. Tissue staining with the laminin antibody disclosed progressive changes with increasing preservation intervals. Staining with the factor 8 antibody demonstrated also progressive changes, but failed to reflect in a gradual fashion increasing endothelial cell injury. Histologic injury became more pronounced after transplantation and reperfusion, then showing destruction of epithelial cells; the extent of injury correlated with the duration of preservation. Glutaminase activity was maintained after cold storage, indicating that the enterocytes remained intact during this period, but when assayed after reperfusion, glutaminase decreased with increasing preservation intervals and increasing histologic mucosal damage. We conclude that cold ischemic injury involves primarily the endothelium and the basement membrane, which progresses to global mucosal impairment with reperfusion.