Epidermal growth factor is normally produced in the salivary gland and Brunner's gland, and is known to exert a protective effect on gastrointestinal mucosa, with which the heling process of gastroduodenal ulcer is expected. Epidermal growth factor also involves in the process of liver regeneration, and the increase of serum epidermal growth factor after the partial hepatectomy has been experimentally documented. This experiment was conducted to examine whether a partial hepatectomy may facilitate the healing of the experimentally induced gastric or duodenal ulcer. The ulcer was induced by applying glacial acetic acid on the gastric serosa for 20 seconds or 75% acetic acid on the duodenal serosa for 5 seconds. All five hepatectomized rats revealed near complete healing of the gastric ulcer within 6 days after ulcer induction while three out of four showed residual ulcer in control (non- hepatectomized) animals. However, the sizes of duodenal ulcers in both groups were not different. We assume that endogenous epidermal growth factor liberated during the regenerative process in the partial hepatectomized rat is responsible for the promotion of healing process of the gaatric ulcer.