Histamine (B-imidazolylethylamine) is derived from the amino-acid histidine, an almost universal constituent of proteins. It is evolved by decarboxylation in an appropriate medium by bacteria. Koessler and Hanke have shown that certain strains of Bacillus coli and other bacteria are capable of producing histamine from histidine in the presence of an available source of carbon such as glycerol or glucose, plus a source of nitrogen (potassium nitrate, ammonium chloride or both) in the presence of oxygen. They believe that histamine is formed in the bowel by bacteria in order to neutralize an excessive acidity produced from glycerol. These observers have shown that histamine is a normal constituent of the cecum and feces of man in sufficient amounts to be dangerously toxic. The reason for the absence of toxicity is not established definitely. Hanke and Koessler1 believe that histamine is rendered pharmacologically inert in its passage through the intestinal wall. It