Reactivity of anti-erythrocyte membrane (RBCm) antibody in sera of B. gibosni-infected dogs on native RBCm and erythrocyte surface (RBCs) was examined using an enzyme linked immunosorbent assay. Anti-RBCm antibody attached to native RBCm and the surface of erythrocytes (RBC) treated with phenylhydrazine or neuraminidase, but not to the surface of non-treated RBC. Based on these results, anti-cytoskeletal protein antibody in sera of B. gibsoni-infected dogs is considered to attach to native RBCm, and furthermore free radical-induced oxidative stress imposed on RBC and sialic acid removal from glycoproteins of RBC are considered necessary for anti-transmembrane protein antibody in sera of B. gibsoni-infected dogs to be bound to RBCs. These are important to elucidating the mechanism of the marked increase in RBCs-bound IgG value and anemia in B. gibsoni infection.