In a previous report we suggested that T antigen appeared to be associated with gastric carcinoma. To verify this hypothesis and characterize the pattern of expression of simple-mucin type carbohydrate antigens (Tn,sialyl-Tn and T before and after neuraminidase) in normal gastric mucosa and precursor lesions of gastric carcinoma, we studied the mucosa adjacent to 100 cases of gastric carcinoma, gastric biopsies of 60 dyspeptic patients, eight adenomatous polyps and eight hyperplastic polyps. The expression of the antigens was more related to the cell type and underlying lesions than to the coexistence of carcinoma. The most distinctive findings concerned intestinal metaplasia, dysplasia and hyperplastic lesions. In intestinal metaplasia, Tn was found mostly in columnar cells and sialyl-Tn in goblet cells. T was more prevalent in incomplete intestinal metaplasia than in complete. A high prevalence of sialyl-Tn expression and cell membrane immunoreactivity for T antigen, similar to those previously found in gastric carcinomas, were observed in three adenomatous polyps, one hyperplastic polyp, five cases of adenomatous dysplasia in the neighbourhood of intestinal carcinomas and four cases of marked foveolar hyperplasia, three of which were from the mucosa adjacent to diffuse carcinomas. We conclude that adenomatous and hyperplastic lesions share with gastric carcinomas features of aberrant glycosylation, namely the cell membrane expression of T antigen.