It has been postulated that endothelial cell adhesion molecules involved in leukocyte recruitment play a role in metastasis. Using an in vitro flow model, we studied the adhesion of the human colon carcinoma cell line KM12-L4 to P-selectin, an inducible endothelial-expressed adhesion molecule involved in leukocyte recruitment. Recombinant forms of P-selectin and Chinese hamster ovary cells stably expressing P-selectin supported attachment and rolling of KM12-L4 cells at 1 to 2 dynes/cm2. The adhesive interactions to P-selectin were abolished by pretreatment of the KM12-L4 cells with neuraminidase but were unaltered by pretreatment of the KM12-L4 cells with O-sialoglycoprotein endopeptidase, an enzyme that cleaves mucin type glycoproteins such as P-selectin glycoprotein ligand-1 (PSGL-1). PSGL-1 is the only counter-receptor for P-selectin known to mediate myeloid cell adhesion to P-selectin under flow. Flow cytometric and Northern blot analyses revealed that KM12-L4 cells did not express PSGL-1 and monoclonal antibody PL1, a function-blocking monoclonal antibody to PSGL-1, had no inhibitory effect on KM12-L4 adhesion to P-selectin under flow. Compared with HL-60 cells, which express PSGL-1, the KM12-L4 cells exhibited a slightly lower rate of attachment to P-selectin and rolled at a significantly higher velocity. In summary, KM12-L4 human colon carcinoma cells interact with P-selectin, under flow, through a PSGL-1-independent adhesion pathway.