The plasma levels of somatostatin (SS) and gastrin (Gas) were investigated in 55 cases of gastric ulcer (GU) and duodenal ulcer (DU) patients. The SS concentration increased significantly as compared with controls. No difference exists between the GU and DU group. The Gas concentration of ulcer patients did not differ from that in controls. There was no significant correlation of the SS and Gas levels. Neither SS nor Gas changed further in the states of ulcer bleeding, helicobacter pylori (Hp) infection and H_2-receptor antagonist treatment.