(Histamine)Diamine oxidase (DAO) is an enzyme that catabolizes a variety of substrates including histamine and diamines. It is the degradative enzyme in the catabolic pathway of polyamines found in high activity in the mature upper villus cells of the rat intestinal mucosa (Luk et al., 1983; Wolvekamp and Debruin, 1994). Blood DAO activity has been well correlated with DAO activity in the villi of the small intestinal mucosa and also with the severity of small intestinal mucosal lesions