To better deinfe the pathogenetic relationship between gastric acid secretion, serum gastrin levels and acute gastroduodenal disease in burned patients, fasting serum gastrin levels were correlated with the results of a nonaugmented gastric analysis performed in 31 hemodynamically stable burned patients. Gastroduodenoscopy documented the status of the gastric and duodenal mucosa at the time of acid analysis and serum gastrin collection. Patients (22) had acute gastroduodenal disease. Diffuse, superficial, gastroduodenal erosions were present in 17 patients; 5 additional patients had ulcerative lesions. Nine patients had normal endoscopic examinations. Gastrin levels were not predictive of the incidence, severity or location of disease. Gastric acidity did correlate with disease severity (correlation coefficient, r = + 0.41, P < 0.05) being lowest in normal persons, intermediate in superficial disease and highest in ulceration. There was no correlation between the levels of serum gastrin and gastric acid secretion. The relative hyperacidity in patients with acute gastroduodenal disease suggested that acid may be 1 factor potentiating mucosal injury in these patients and may be particularly important in the evolution of life-threatening ulceration.