We developed an easy enzyme-linked immunosorbent assay (ELISA) for anti-mitochondrial antibodies, and detected high levels of anti-mitochondrial antibodies in MRL/Mp-lpr/lpr (MRL1 /1) mice. The influence of the presence of anti-DNA antibodies in the tested sera on this assay was also evaluated. The monoclonal anti-DNA antibodies, which were made from non-immunized MRL1 /1 mice, did not react with the mitochondrial antigens adhering to polystyrene plates. Absorption with DNA had little effect on the levels of mitochondrial antibodies in MRL1 /1 sera. Our assay for mitochondria-binding antibody was very easy and sensitive, although it could not differentiate among heterogeneous anti-mitochondrial antibodies.