Vibrio vulnificus is a Gram-negative bacterium that causes a fatal septicemia. One of its virulence factors is a membrane-bound lipoprotein, IlpA, which can induce cytokine production in human immune cells. In the present study, the role of IlpA as an adhesion molecule was investigated. An ilpA-deleted V. vulnificus mutant showed significantly decreased adherence to INT-407 human intestinal epithelial cells, which in turn resulted in reduced cytotoxicity. The DeltailpA mutant recovered the adherence ability of the wild type by complementation in trans with the intact ilpA gene. In addition, pretreatment of V. vulnificus with anti-IlpA polyclonal antibodies resulted in a significant reduction of bacterial adherence. To localize the domain of IlpA required for cytoadherence, three truncated recombinant IlpA polypeptides were constructed and tested for the ability to adhere to human cells by a ligand-binding immunoblot assay and fluorescence microscopy. The polypeptide containing the carboxy (C)-terminal hydrophilic domain exhibited direct binding to INT-407 cells. Therefore, the C-terminal domain of IlpA allows this protein to be an adhesion molecule of V. vulnificus.