We invistigated the sequntial changes in plasma and intestinal diamine oxidase (DAO) levels in animals and patients after burn injury. The results were as follows: 1. The plasma DAO level in patients was increased significantly at 1, 3, 7, 14 d and returned to normal at 21 d postburn; 2. In pigs, the elevation of plasma DAO level was also found during the whole experiment, but only significantly so at 72 h postburn; 3. In scald rats, the DAO level was increased in plasma and decreased in intestine. The above results suggested that intestinal mucosa injury and DAO release into blood occurred after burn injury. The activity of DAO in plasma might be one of the marker to reflect injury of intestinal mucosa.