Babesia bovis merozoites are exposed to antibodies during the extraerythrocytic phase, and surface polypeptides bearing exposed epitopes are possible immunogens. Monoclonal antibodies reactive with the merozoite surface bind either immunodominant epitopes expressed diffusely on the merozoite surface or, alternatively, epitopes expressed in a polar pattern. Epitopes expressed diffusely on the immunodominant 42- and 44-kDa merozoite polypeptides were not conserved among strains from geographically diverse regions. In contrast, epitopes expressed in a polar pattern on the merozoite surface were conserved among nine strains and clones. Identification of variables and conserved epitopes provides a basis for defining antigenic variation and cross-protective immunity.