Pepsinogen level, expressed as the potential peptic activity of pepsinogen was determined by a fluorescent microassay using succinyl albumin as substrate, in biopsy specimens from the gastroduodenal mucosa of 95 subjects. The following results were obtained: (1) pepsinogen level in the gastric mucosa becomes progressively higher from pylorus to corpus (p < 0.001); (2) pepsinogen level in the gastroduodenal mucosa of duodenal ulcer was significantly higher than that of normal mucosa or gastric ulcer (p < 0.001); (3) the difference in pepsinogen level between the gastric mucosa with and without intestinal metaplasia was statistically significant (p < 0.01); (4) the correlation between the histology of gastric glands and pepsinogen level was fundic gland > intermediate gland > pyloric gland (p < 0.001).