Quantitative studies on the binding of concanavalin A (Con A) and wheat-germ agglutinin (WGA) to a series of rat hepatocarcinoma metastatic variants revealed a positive correlation between the amount of cell-surface-bound lectin and lung colonization potential. Scatchard analysis of Con A and WGA binding to 10 individual clones isolated from a subcutaneous (s.c.) tumor transplant and to tumor-cell isolates from 10 individual spontaneous lung metastases from the same animal showed diverse binding characteristics for these cell populations. Nevertheless, the expression of Con A receptor sites accurately predicted the lung colonization potential of 3 isolates from the lung metastases. Higher lectin binding curves were observed for the clones from the subcutaneous tumor than for the isolates from lung metastases. These data suggest that a high Con-A binding potential is indicative of a high lung colonization potential for these hepatocarcinoma cells, but that this phenotype may be rapidly lost during tumor outgrowth in the lungs. The binding of tumor cells to vascular endothelial cell monolayers was inhibited in the presence of Con A; however, no inhibition was observed with 2 other lectins. Attachment of tumor cells to endothelial cell monolayers was also inhibited by the monosaccharides methyl alpha-D-mannopyranoside and N-acetyl-D-galactosamine. Other monosaccharides tested did not alter the attachment of tumor cells to endothelial cell monolayers.