I investigated the possibility of production of antibody to bacterial membrane-cardiolipin using cardiolipin micelles, Staphylococcus aureus (S.aureus) and L-form of S. aureus. I also investigated and the reactivity of anti-cardiolipin (CL) antibody with bacteria and DNA.I confirmed that the bacterial membrane-cardiolipin induced the production of anti-CL antibody, which was present mainly in the IgM fraction, but also in the IgG fraction.The anti-CL antibody reacted with L-form of bacteria and bacterial membrane fractions, but it did not react with the vegetative form of bacteria other than S. aureus nor with DNA. On the basis of these findings, I considered that the L-form of bacteria or fragments of bacterial membranes can be detected by immunofluorescence antibody technique or nitrocellulose membrane-enzyme immunoassay using the anti-CL antibody.