An untreated canine hepatic homograft is shown six days after transplantation (left). Portal veins (clear spaces) and central vein (arrow) are surrounded by dense cellular infiltration and there is centrilobular necrosis with hemorrhage (hematoxylin and eosin stain, ×30). Photo at right shows normal liver architecture in another canine homograft one year after transplantation. This dog received azathioprine for four months, no additional therapy. It is still alive after some seven years.