Levels of plasma amino acids, ammonia, glucagon and insulin and their 5-hr responses to a protein feeding were evaluated before and sequentially (3 mo and 1 yr) after distal splenorenal shunt in 10 patients with cirrhosis belonging to Child-Pugh's class A or B. An index of glucagon effectiveness (plasma glucose/glucagon) was also calculated. These parameters were related to liver test results, portal vein diameter and mental state, and they were compared with those found in seven patients undergoing sclerotherapy of esophageal varices with comparable liver function (control group). Liver test results and levels of plasma insulin did not change in either group. Shunt significantly increased levels of fasting tyrosine, methionine, ornithine, arginine, histidine, ammonia and glucagon with respect to the control group; it also significantly decreased levels of leucine, valine, glucagon effectiveness and portal vein diameter. The elevation of levels of tyrosine, ammonia and the sum of arginine and ornithine was correlated directly with the increase in glucagon and inversely with the decline in glucagon effectiveness. Tyrosine increase was also correlated with the reduction of portal vein diameter. One shunted patient showed mild hepatic encephalopathy. Protein feeding did not worsen the mental state of patients before and after the operation. Surgery significantly increased the 5-hr response to the meal of gluconeogenic amino acids; its rise was again correlated with the changes in glucagon plasma levels and effectiveness. Although the absorptive levels of plasma ammonia were significantly higher 1 yr after surgery, its 5-hr response barely rose. In cirrhotic patients with a relatively preserved liver function, distal splenorenal shunt progressively worsened the fasting plasma profile of nitrogen compounds and the response to protein ingestion of gluconeogenic amino acids. The decline of portal blood flow and glucagon effectiveness may be causal factors. Despite this, the “cerebral” tolerance to a moderate oral load of protein was not reduced by surgery. (Hepatology 1994;19:329–338).