The endogenous mucosal PG levels (PGE2, PGF2 alpha, PGI2, TXB2) of the gastric stump were investigated from biopsy materials, after partial gastrectomy made for ulcer disease. The mucosa of the stomach remnant were found to contain mainly PGE2 and PGI2. The PG contents of the mucosa of gastric stump were not influenced by the type of resection. Mucosal PG concentrations on the greater curvature were not dependent on the patients' age, the indication of the gastrectomy, the duration of postoperative interval, or the sex of the patient. There was no relation between the secretion capacity of the resected stomach and the mucosal PG contents of the greater curvature. After Billroth I and II gastrectomy procedures equivalently fair correlations have been established between the mucosal levels of PGE2 and PGF2 alpha, PGE2 and TXB2, PGF2 alpha and TXB2, PGI2 and TXB2 on the greater curvature, respectively. After both types of gastrectomy the mean PGI2 mucosal concentration of the greater curvature was significantly lower than those of the gastroenteroanastomosis and lesser curvature below the cardia, which in turn did not differ from each other. Biliary reflux does not cause characteristic alterations of the mucosal PG levels on the greater curvature. No definite relation between the histological findings of the mucosa and the PG concentrations was observed, which suggests a secondary role of the endogenous PGs in the pathogenesis of light microscopic mucosal alterations of the resected stomach.