The expression of MUC1 and MUC2 mucin peptide core antigens in gastric carcinomas was studied by immunohistochemistry to determine correlations with TNM stage and histo-pathological classifications as well as a possible prognostic impact. Paraffin-embedded specimens from 128 gastric carcinomas with a minimal follow-up of 5 years were immunostained. In addition to a polyclonal antiserum generated against polymorphic epithelial mucin (MUC1) from human milk, 2 monoclonal antibodies (MAbs), HMFG2 (anti-MUC1) and 4FI (anti-MUC2), were applied. Reactivity of carcinomas was correlated with the classifications of the UICC (TNM), WHO and Laurén. Correlations with overall survival were analyzed using the Kaplan and Meier product limit method. MUC1 immunoreactivity was associated with an advanced pTNM stage. The demonstration of both mucin species (MUC1, MUC2) displayed a statistically significant correlation with tubular/papillary vs. signet-ring cell differentiation as well as with intestinal-type vs. diffuse-type of tumor growth according to Laurén. In particular, MUC2 was only rarely detectable in signet-ring cell and diffuse-type tumors. MUC1 correlated with poor prognosis in all cases and the subgroup of stage I tumors. According to the histopathological classifications, a similar result was observed in signet-ring cell and diffuse-type carcinomas. In contrast, MUC2 reactivity was associated with a favourable prognosis of intestinal-type carcinomas. In the non-neoplastic gastric mucosa, both peptide cores were recognized in the superficial epithelium, whereas parietal cells contained only MUC1, and intestinal metaplasia almost exclusively MUC2 antigens. We conclude that the mucin peptide core antigens are suitable markers for the tubule-rich gastric carcinomas, which may in part be derived from intestinal metaplasia. In addition, MUC1 may exert a prognostic relevance and appears to be involved in the progression of diffuse-type tumors.