Endogenous lectins purified from UV-2237-IP3 murine fibrosarcoma cells by affinity chromatography consisted of two polypeptide species of Mr 14,500 (L-14.5) and Mr 34,000 (L-34). Antibodies against this material immunoprecipitated the lectins from cells radiolabelled on the cell surface as well as in the cytoplasmic compartment. Similar analyses of normal rat embryonal fibroblasts revealed the presence of only the L-14.5. In contrast, both L-14.5 and L-34 were found in oncogene-transfected, immortalized cell clones derived from the normal rat cells, as well as in untransformed BALB/c-3T3 clone A31 and its descendant subclones selected for expression of the transformed, the tumorigenic and the metastatic phenotypes. Among the cells constituting the latter system, a marked increase in the amount of cellular and cell-surface lectins was observed upon progression to the metastatic phenotype. These results suggest that the expression of endogenous tumor-cell-surface lectins is associated with transformation and metastasis.