Serum anti-erythrocyte membrane (RBCm) antibodies and anti-RBCm antibodies eluted from erythrocytes of Babesia gibsoni-infected dogs were examined for immunologic characteristics by immunoblotting analysis. Serum anti-RBCm antibodies of the dogs before and after the experimental inoculation with parasitized erythrocytes reacted with cytoskeletal (bands 1, 2, 2.1, 4.1, 4.2 and 5) and transmembrane structural (band 3) proteins of either self or non-self RBCm. Anti-RBCm antibodies eluted from erythrocytes of B. gibsoni-infected dogs reacted with bands 3 and 4.2 of self and non-self RBCm.