The level of plasma postheparin-diamine oxidase was determined in two patients three days after an anaphylactic shock and was controlled four weeks, and also six months later. A decrease of the enzyme levels to about 10% of a control group was found and a slow enzyme increase to about 40% observed six months later. It seems probable that in anaphylaxis a depletion of the enzyme in liver and small intestine occurs as could be shown in animals after heparin load.