We have analyzed cell surface-bound carbohydrates in two different model systems for metastasis composed of closely related tumor cell lines with differing metastatic potential. The first system studied was that of the DBA/2-derived T-lymphoma lines (Eb/ESb) and some recently established sublines of ESb with altered metastatic behavior (ESb-M and ESb-MR). The second system consisted of the highly metastatic MDAY-D2 cells, a wheat germ agglutinin-resistant low metastatic subline MDW40, and two metastatic revertants from the latter. The cells were stained with fluorescein isothiocyanate-conjugated lectins and analyzed by flow cytofluorography. All low-metastatic tumor lines expressed receptor sites for the lectins soybean agglutinin (SBA) and Vicia villosa (VV). The metastatic lines had the respective lectin binding sites blocked by sialic acid (SA). A good correlation was found within the cell lineages Eb leads to ESb leads to ESb-M leads to ESb-MR and MDAY-D2 leads to MDW40 leads to MDW40M1 between reactivity of SBA and VV and metastatic potential. The amount of neuraminidase-accessible SA was similar for all cell types (except MDW40) indicating differences in the positioning of SA. For high-metastatic ESb cells, the sialylation of SBA and VV receptor sites was paralleled by a relative decrease of SA associated with receptor sites for peanut agglutinin. Low-metastatic Eb cells, in contrast, had their peanut agglutinin receptor sites sialylated but expressed asialylated SBA and VV receptor sites. Eb cells were also found to have 2-fold higher activities in galactose-specific sialyltransferases. It is proposed that the differences in positioning of SA on the cell surface leading to masking or unmasking of terminal sugars could influence the metastatic potential of tumor cells.