This study was conducted to investigate the effect of the ingestion cf rice and hamburger meals upon plasma gastrin concentration in normal subjects and patients with ducdenal ulcer or gastric ulcer. The subjects including 19 patients with duodenal ulcer (mean age:42.9, range: 18-73 years) and 11 with gastric ulcer (mean age:42.9, range: 21-54 years), and 19 normal persons (mean age: 26. 8, range: 17-40 years) without recogni zed gastrointestinal disease were studied. The patients were radiologically and endcscopically diagnosed by inpatient service at St. Marys Hospital and St. Vincent's Hospital. After an overnight (about 15 hours) fast, 10 duodenal ulcer patients, 11 gastric ulcer patients and 9 normal control subjects ingested a rice meal, and the remaining 9 patients with duodenal ulcer and 10 control subjects ingested a hamburger meal. The rice meal consisted of 300g boiled rice, 150 g vegetables and one egg, corresponding to 19 g protein, 22 g fat and 120 g carbohydrate and the hamburger meal consisted of 200 g hamburger, 50 g vegetables and 200 ml milk, corresponding to 43 g protein, 43 g fat and 9 g carbohydarte. The venous blood samples were drawn before and after the ingestion of the test meal for the measurement of gastrin by means of radioimmunoassay. 1. Plasma gastrin concentration in response to the ingestion of a hamburger meal increased significantly in the control subjects and the patients with duodenal ulcer compared with the fasting concentration in the control subjects and the patients, the postprandial value of the patients with duodenal ulcer being significantly higher than that of the control subjects. 2. After the ingestion of a rice meal, plasma gastrin concentration in the control suhjccts, the duodenal ulcer patients and the gastric ulcer patients increased significantly compared with the fasting value in each subjects. The postprandial plasma gastrin concentrations in these patients rose significantly above the normal level. There was no significant difference between the duodenal ulcer and the gastric ulcer patients in the postprandial concentration. 3. Although fasting plasma gastrin concentration of the patients with duodenal ulcer alone was significantly higher than that of the control subjects, the fasting gastrin concentration of the gastric ulcer patients also had a tendency to increase compared with that of the control subjects. There was no significant difference statistically between the duodenal ulcer and the gastric ulcer patients in the fasting value. It is inferred from the above results that the hypersecretiori of gastrin is closely related with the peptic ulcer, especially duodenal ulcer.