Two anti-sialyl Lewis X (sLeX) monoclonal antibodies, mAb FH6 and mAb KM93, were analyzed by flow cytometry for their ability to bind to 16 human colon carcinoma cells. The binding profiles of these two anti-sLeX monoclonal antibodies did not correspond to each other. Three of the cell lines were reactive with mAb FH6 but not with mAb KM93. These three cell lines did not adhere to Chinese hamster ovary cells that were stably transfected with human E-selectin cDNA in an E-selectin-dependent manner. In contrast, almost all human colon carcinoma cell lines that bound to mAb KM93 adhered to cells that expressed E-selectin. These results suggest that a subtype of sLeX carbohydrate epitopes recognized by mAb FH6 do not always function as ligands for E-selectin.