Treponema denticola is a gram-negative anaerobe that can cause periodontal disease. The adhesion of this bacterium to host tissues is considered to be the primary event in the colonization and infection of a host. Fibrinogen is generally found in damaged tissues resulting from periodontitis. The binding ability of T. denticola to fibrinogen may therefore be an important virulence factor in inducing periodontal diseases. It has been reported recently that oral spirochetes can be labeled with fluorescent fatty acids and we speculated that this labeling method could be used in an oral spirochete binding assay. The binding of several different strains of T. denticola to immobilized human fibrinogen was therefore tested using the fluorescent fatty acid labeling method. In the case of immobilized fibrinogen, the T. denticola ATCC 35405 strain showed saturable binding to immobilized fibrinogen. Indeed, all four different T. denticola strains tested in this experiment, T. denticola ATCC 35405, T. denticola ATCC 33520, T. denticola ATCC 35404 and T. denticola OTK showed binding to fibrinogen. The fluorescent fatty acid labeling method thus shows utility in binding assays for T. denticola, different strains of which can generally bind to immobilized fibrinogen.