The pattern of intermediate filament protein expression was studied in tumor cell variants of the BSp73 spontaneous rat adenocarcinoma of the pancreas exhibiting distinct morphology and metastatic phenotype. The non-metastasizing AS cells which adhere and spread on a solid substrate express only the vimentin type mesenchymal intermediate filament protein. The ASML metastatic cell variant which adheres but does not spread on the substrate expresses a complex pattern of cytokeratins characteristic of the adenocarcinoma of the pancreas and a low level of vimentin. The differences in the expression of the intermediate filament proteins between the variants were also reflected at the level of the corresponding mRNAs as revealed by RNA blot analysis with complementary DNA clones specific to vimentin and the acidic as well as the basic cytokeratin subfamily. When the two cell variants were cultured for 72 h in suspension culture on nonadhesive substrata the AS cells responded with a marked reduction in their vimentin synthesis. The ASML variant cells which are characterized by a round configuration in both monolayer and suspension culture continue to synthesize the same intermediate filament proteins under both culture conditions. The relationships among environmental conditions that affect cell shape and contacts, the shifts in the expression of intermediate filaments, and the metastatic property of tumor cells are discussed.