Porphyromonas gingivalis is a periodontopathogen that may play a role in cardiovascular diseases. Hemagglutinins may function as adhesins and are required for virulence of several bacterial pathogens. The aim of this study was to determine the role of hemagglutinin B (HagB) in adherence of P. gingivalis to human coronary artery endothelial (HCAE) cells. P. gingivalis strain 381, a P. gingivalis 381 HagB mutant, Escherichia coli JM109 expressing HagB (E. coli-HagB), and E. coli JM109 containing pUC9 (E. coli-pUC9) were tested for their ability to attach to HCAE cells. Inhibition assays were performed to determine the ability of purified recombinant HagB (rHagB) as well as antibodies to HagB, including the polyclonal antibody (PAb) A7985 and the monoclonal antibody (MAb) HL1858, to inhibit the attachment of P. gingivalis to HCAE cells. As expected, when the attachment of P. gingivalis and the HagB mutant were compared, no statistical significance was observed between the two groups (P = 0.331), likely due to the expression of the hagB homolog hagC. However, E. coli-HagB adhered significantly better to HCAE cells than did E. coli-pUC9, the control strain. In a competition assay, the presence of purified rHagB decreased bacterial adhesion of P. gingivalis or E. coli-HagB to HCAE cells. The presence of PAb A7985 or MAb HL1858 also significantly decreased attachment of P. gingivalis and E. coli-HagB to host cells. These results indicate that HagB is involved in the adherence of P. gingivalis to human primary endothelial cells.