Immunohistochemical screening of gastric adenocarcinomas from 42 different patients revealed variant CD44 expression in all specimens tested. Adenocarcinomas of the intestinal type were strongly positive for epitopes encoded by variant exons v5 and v6, whereas diffuse-type adenocarcinomas predominantly expressed only exon v5. Normal stomach mucosa was stained by an exon v5-specific monoclonal antibody within the foveolar proliferation zone and on mucoid surface epithelium. Areas of intestinal metaplasia reacted positively with monoclonal antibodies specific for exons v5 and v6. Analysis of RNA expression revealed dramatic differences between normal mucosa and adenocarcinomas. Whereas in normal epithelium only two CD44 variant RNAs containing exons v5 and/or v6 could be detected, intestinal-type tumors yielded a much more complex pattern of amplification products which hybridized to exons v5 and v6. A similar complex expression pattern of CD44 variants was observed in three cell lines established from intestinal-type tumors. In a sample of a diffuse-type tumor, expression of exon v5, but not v6, could be detected, confirming the data obtained with immunohistochemistry. These differences in variant exon v6 expression observed between diffuse-type and intestinal-type stomach adenocarcinomas establish variant CD44-specific antibodies as a tool in gastric cancer diagnosis and also support the theory of different origins for these tumor types.