The pig shows a marked response to end-to-side portacaval shunt. Survival is short and levels of alkaline phosphatase and cholesterol fall. This study was designed to determine the role of the reduced food intake which follows the operation upon these results. In pair-fed, sham-operated pigs, survival was short and levels of alkaline phosphatase and cholesterol also fell. Sham-operated animals fed normally did not show this response. Reduced appetite has been recorded in many experimental animals after portacaval shunt, but the cause remains to be elucidated. Encephalopathy, bacteremia, peptic ulceration, or hormonal imbalance could be implicated. Similar alteration in appetite and weight loss have not been observed in children who have been treated by portacaval shunt for glycogen storage disease or hypercholesterolemia; however, the underlying metabolic disorder or the species difference may be a contributory cause.