The fasting serum gastrin levels were measured by radioimmunoassay in 32 normal healthy subjects without recognized gastrointestinal symptoms and 93 patients with various gastric diseases, who were visited of admitted to National Medical Center from February to June, 1981. The following results were obtained; 1) The fasting mean serum gastrin level in normal subjects was 55.9+-26.3 pg/m1, and there was no difference between male and female. 2) The gastrin levels in gastric and duodenal ulcer were 85.0+-28.4 and 76.0+-43.0 pg/ml respectively, and it's values were elevated as compared with normal subjects. In gastric ulcer, the gastrin level was elevated than that of duodenal ulcer, but no significant difference in each other. 3) The gastrin level in stomach cancer was 89.5+-42.2 pg/ml, and it's values were markedly elevated as compared with values in normal subjects. 4) The gastrin level in gastritis was 73.4+-37. 4 pg/ml, and it's values were elevated as compared with values in normal subjects. 5) The gastrin level in post-gastrectomy state was 50.3+-16.3 pg/ml, and it's values were slightly decreased as compared with values in normal subjects.