For a variety of reasons, the dog has been the conventional experimental animal for the study of hepatic physiology and portal hemodynamics. There are important differences, however, in basic hepatic anatomy and physiology between man and dog. These differences make it difficult to transfer laboratory data obtained from dog experiments to clinical problems dealing with patients. For example: 1. Nutritional cirrhosis has not been produced in the dog. 2. Ligation of the portal vein in the dog carries with it a mortality rate which approaches 100%. 3. Canine hepatic veins contain well-developed smooth muscle bundles which are capable of sphincteric action and can produce physiologic "outflow block"1 in response to nervous or drug stimulation. This anatomical arrangement is not seen in man. 4. Esophageal varices created experimentally in the dog lie in the outer esophageal wall, rather than submucosally.2 In contrast, the Macaca mulatta monkey more closely resembles