PGE2-like immunoactivity was measured radioimmunologically in specimens from gastric corpus mucosa in (a) healthy subjects, (b) patients without liver disease in the absence or presence of gastric ulcer, and (c) patients with alcoholic cirrhosis in the absence or presence of gastric ulcer, further divided into subgroups without or with portal hypertension. The PGE2-like immunoactivity was almost the same in subjects without liver disease and in cirrhotic patients without portal hypertension. A significantly decreased PGE2-like immunoactivity was found in patients with portal hypertension, especially in cases of congestion in the mucosa. A further decrease of the PGE2-like immunoactivity could be found whenever gastric corpus ulcer was present. This decrease is statistically significant. We therefore concluded that a decrease in the PGE2-like immunoactivity in the gastric mucosa of cirrhotic patients is closely related to portal hypertension. Congestion in the mucosa, thought to be a relevant factor in the pathogenesis of the mucosal PGE2 deficiency, might also play a role.