In a control group (n = 12) the histamine content of the liver was 1.42 microgram/g tissue and the activity of the histamine-degradating enzyme, HMT, 421.5 pmol/(min . mg protein). In patients with affections of the biliary tract (n = 12) the histamine content was significantly raised to 3.09 microgram/g tissue and the HMT activity slightly diminished [349 pmol/(min . mg protein)]. The lowest values of HMT activity were found in the livers of those patients with histologically proven damage of liver cells.