With the aid of an image processor, the length of the intestinal metaplasia (IM) was recorded in 33 gastrectomy specimens (23 with early gastric cancer and 10 with gastric peptic ulcer). A total of 1917 sections were analyzed. The length of the areas with IM and the total length of the muscularis mucosa were measured in individual sections. The resulting ratio (length of IM/length of muscularis mucosa) was noted as the intestinal metaplasia index (IMI), as an expression of the extension of IM in the specimens. The IMI was influenced by the age of the patient and by the histologic type of the tumor: a higher IMI was found among older patients and among patients with adenocarcinoma of intestinal type. A comparison with a similar study done in gastrectomy specimens from Swedish patients indicates that despite the latter group being older, and the tumors being more advanced, the IM was much more extended in the gastric mucosa of the Japanese patients with gastric adenocarcinomas of intestinal type. From the results it is suggested that extended IM in the gastric mucosa may have some bearing on the histogenesis of gastric carcinomas, particularly adenocarcinomas of intestinal type.