The basal acid output (BAO), post-pentagastrin acid output (MAO), fasting and post-prandial gastrin levels in 40 patients with proven cirrhosis of the liver were compared with those in 20 normal controls. The mean BAO and MAO were significantly lower than normal, the mean fasting gastrin level was significantly higher than normal, and the postprandial gastrin response was significantly increased and prolonged. These differences were still significant even when the patients were divided into cryptogenic and alcoholic subgroups. A significant inverse relationship between MAO and the integrated gastrin response to meal was observed both in the normal controls and in the cirrhotic patients. The MAO and integrated gastrin response of the cirrhotic patients did not correlate with the degree of liver function impairment. In five cirrhotic patients fasting and postprandial gastrin levels were unchanged after splenorenal shunt operation. A more consistent abnormality of the gastric mucosa as assessed by endoscopy and biopsies appeared to be mucosal congestion with occasional atrophic gastritis. the severity of mucosal abnormality, however, was unrelated to the degree of hypoacidity. these results indicate, firstly, that the hypergastrinaemia in cirrhotic patients is a reflection of gastric hypoacidity and bears no direct relationship to hepatic dysfunction. Secondly, the gastric hypoacidity does not accrue solely from mucosal abnormality. It is suggested that this hypoacidity may result from the presence of excessive amounts of circulating acid-inhibiting intestinal peptides, which the diseased liver fails to metabolise.