Diffuse erosive "gastritis" was discovered as early as five hours postinjury in 45 of 54 burn patients (83.5%) evaluated by gastroduodenoscopy. Acute ulcers were identified in 14 patients (26%); concomitant duodenal disease was present in 34 patients (76%). Microvascular fibrin thrombi were not demonstrated even though five patients had disseminated intravascular coagulation. Seven patients were examined before nasogastric intubation; four, with a mean burn size of 59.6% total body surface, had diffuse "gastritis." Low total serum protein levels were measured in 81% of tested patients, but were not predictive of mucosal disease. Hemorrhage followed the clinical deterioration of six patients (11.1%); one ulcer perforated. Whereas coagulation abnormalities, nasogastric intubation, and hypoproteinemia may augment mucosal injury, the morphologic and histologic examinations of the lesions suggested a primary ischemic cause resulting from the opening of submucosal shunts or local vasoconstriction.