We examined the expression of carbohydrate antigens which are associated with the earliest steps in mucin glycosylation (Tn and sialosyl-Tn) and the expression of the mucin core protein antigens associated with MUC1 gene product (DF3 antigen) as well as MUC2 gene product (intestinal-MRP antigen) in tissues from 38 patients with carcinoma of the ampulla of Vater, in order to determine whether these mucin antigens are available as tumor markers or not, and to evaluate whether their expression is correlated with the biological behavior of the carcinomas or not. DF3 antigen showed a relatively high expression rate (61%) in the carcinoma tissues, but was rarely expressed in the non-neoplastic epithelium around the carcinomas in the region of the ampulla of Vater. Tn and sialosyl-Tn antigens showed high expression rates in the carcinoma tissues (86% and 84% each), whereas they showed rare or no expression in the non-neoplastic epithelium around the carcinomas, except for highly restricted expression in the duodenal villous epithelium. The patients with positive DF3 expression in the carcinoma showed significantly poorer survival than those with negative DF3 expression (P < 0.05), whereas the patients with positive intestinal-MRP expression in the carcinoma showed significantly more favorable survival than those with negative intestinal-MRP expression (P < 0.05). The expression rate of DF3 antigen was significantly higher in the cases with deep invasion into the pancreas (89%) than in those with no or minimal invasion (52%) (P < 0.05). In contrast, the expression rate of intestinal-MRP antigen was significantly higher in the cases with no or minimal invasion into the pancreas (38%) than in those with deep invasion (0%) (P<0.05). In conclusion, the expression of DF3, To and sialosyl-Tn antigens is an effective histopathological indicator for carcinomas in the area of the ampulla of Vater, and the expression of DF3 and intestinal-MRP antigens is a useful indicator of the prognosis of the patients.