Engagement of vascular E-selectin and leukocyte L-selectin with relevant counter-receptors expressed on tumor cells contributes to the hematogenous spread of colon carcinoma. We recently demonstrated that the LS174T colon carcinoma cell line expresses the CD44 glycoform known as hematopoietic cell E-/L-selectin ligand (HCELL), which functions as a high affinity E- and L-selectin ligand on these cells. To define the contribution of HCELL to selectin-mediated adhesion on intact tumor cells, we measured the binding of LS174T cells transduced with CD44 short interfering RNA (siRNA) or with vector alone to 6-h interleukin-1beta-stimulated human umbilical vein endothelial cells (HUVEC) and to human peripheral blood mononuclear cells (PBMC) under physiological flow conditions. LS174T cell attachment to HUVEC was entirely E-selectin-dependent, and PBMC tethering to tumor cell monolayers was completely L-selectin-dependent. At physiological shear stress, CD44 siRNA transduction led to an approximately 50% decrease in the number of LS174T cells binding to stimulated HUVEC relative to vector alone-transduced cells. CD44 siRNA-transduced cells also rolled significantly faster than vector-transduced cells on HUVEC, indicating prominent HCELL participation in stabilizing tumor cell-endothelial adhesive interactions against fluid shear. Furthermore, HCELL was identified as the principal L-selectin ligand on LS174T cells, as PBMC binding to CD44 siRNA-transduced tumor cells was reduced approximately 80% relative to vector-transduced cells. These data indicate that expression of HCELL confers robust and predominant tumor cell binding to E- and L-selectin, highlighting a central role for HCELL in promoting shear-resistant adhesive interactions essential for hematogenous cancer dissemination.