Because of its anatomical relationship to the gastrointestinal tract, the normal liver is able to act as a controlling "filter" against the influx of plasma histamine chiefly by uptake and breakdown. This prevents unwanted effects on the systemic circulation. The ability to eliminate histamine from plasma is decreased in cirrhosis. Plasma histamine levels in peripheral venous blood of ten patients with liver cirrhosis and gastric ulcer, proven radiologically and by endoscopy, indicated a significantly higher concentration (1.3 +/- 0.4 micron/1) than in a control group of 16 patients without such disease (0.7 +/- 0.2 micron/1). In a group of patients with fatty liver (stages I-II) there were normal histamine levels (0.7 +/- 0.3 micron/1).