Sucralfate is a basic aluminum salt of a sulfated disaccharide. In this study, patients with gastric ulcer were given oral multiple doses of sucralfate prior to partial gastrectomy, and binding of the drug to the ulcer lesion and to nonulcerated mucosa was estimated by chemical determination of aluminum and sulfated disaccharide. The ulcerated mucosa was found to contain, on the average, 6-7 times more sucralfate per square centimeter than the control mucosa (P less than 0.01 and less than 0.05 for aluminum and sulfated disaccharide, respectively). The high affinity of sucralfate for ulcerated mucosa, particularly the sucrose sulfate moiety, supports previous data that the beneficial effect of sucralfate in ulcer disease is due in part to complex formation between sucrose sulfate and proteins at the ulcer site.