We demonstrated spirochetes from a skin lesion of the erythema chronicum migrans in a patient with
Lyme disease by the murine monoclonal antibody (H9724). Frozen skin biopsy specimens reacted with murine monoclonal antibodies (H5332, H9724, and H4825) and were examined by indirect immunofluorescence assay. The spirochetes stained with monoclonal antibody H9724 and fluorescein isothiocyanate-conjugated second antibody (goat antimouse IgG). The antibody H9724 is specific for the periplasmic flagellae (axial filaments) of several Borrelia species, including Ixodes dammini spirochete (Borrelia burgdorferi). No immunofluorescence staining was demonstrated with either monoclonal antibody H5332, specific for an outer membrane protein of North American strains of B. burgdorferi, or the antibody H4825, specific for an outer membrane protein of B. hermsii.