Extravasation of tumor cells is a pivotal step in metastasis formation. This step is initiated by an interaction of extravasating tumor cells with endothelial cells. Among the molecules mediating tumor-endothelium interactions are selectins and their fucosylated ligands. In a previous study, we demonstrated that the fucose-generating FX enzyme regulates the expression of selectin ligands by B and T lymphocytes and by head and neck squamous cell carcinoma cells. It was also shown that the FX enzyme regulated important interaction parameters between these cancer cells and endothelial cells. The present study was aimed to determine whether the FX enzyme controls adhesive interactions between colorectal cancer cells and endothelial cells. The results clearly indicate that this is indeed the case. Overexpressing the FX enzyme by the transfer of FX cDNA to low FX-expressing colorectal cancer cells resulted in an increased adhesive capacity of the transfectants to activated endothelial cells and to recombinant E-selectin. Down-regulating FX levels in colorectal cancer cells expressing high levels of endogenous FX by transfection with small-interfering RNA resulted in a down-regulated expression of the selectin ligand sialyl Lewis-a and a decrease in the adhesive capacity of the transfectants to activated endothelial cells and to recombinant E-selectin. These transfection experiments also indicated that manipulating the levels of the FX enzyme affected global cellular fucosylation and altered the interaction of colorectal cancer cells with some extracellular matrix components such as fibronectin. We also found that highly metastatic colorectal cancer variants express higher levels of FX and of sialyl Lewis-a than low metastatic variants originating in the same tumors. These results lead us to hypothesize that the FX enzyme controls the capacity of colorectal cancer to extravasate and form metastasis. If this hypothesis will be confirmed the FX enzyme could become a target molecule for metastasis prevention.