Lewis(y) (Le(y)), also designated CD174, represents a carbohydrate blood group antigen which is strongly expressed in neoplastic gastrointestinal tissues. Previous reports indicated an association between Le(y) expression and apoptosis. Therefore, we tried to elucidate its clinicopathological relevance in a series of 160 gastric and 215 colorectal carcinomas by immunohistochemical detection of Le(y) and visualization of apoptotic cells applying the in-situ-end labelling (ISEL) method, followed by semiquantitative scoring of the specimens. In both gastric as well as colorectal carcinomas, between 40 and 50% of the cases were Le(y) reactive. Signet-ring cell carcinomas of the stomach exhibited a significantly stronger Le(y) expression compared to other tumor types. In colorectal cancers, Le(y) was associated with increased tumor staging, showing the strongest positivity in stage IV. Further correlations with clinicopathological variables or prognosis were not observed. On the other hand, the amount of apoptotic cells was significantly reduced in mucinous adenocarcinomas of the colorectum compared to non-mucinous carcinomas. Scoring of apoptotic cells did not result in any other clinicopathologically relevant correlations. In addition, a significant association between Le(y) antigen expression and apoptosis score could not be established. Therefore, the hypothesis of a functional relationship between these two aspects of gastrointestinal tumor biology is not confirmed by our data.