Outer membrane protein preparations have been demonstrated to elicit protective immunity for Anaplasma marginale. Attempts to recreate this protective immunity using known surface proteins have been unsuccessful; therefore, novel outer membrane proteins have been searched for using a proteomic/genomic approach. Annotation of the whole genome sequence identified 62 outer membrane protein candidates based on sequence similarity to known surface proteins. In a proteomics approach for the identification of immunostimulatory outer membrane proteins, outer membrane preparations that were separated on 2D gels were used to immunize calves . Antisera from the calves were used to detect immunoreactive proteins, which were then selected and subjected to mass spectrometric analyses. These data were mapped back to the annotated A. marginale genome and have identified several new outer membrane proteins that are vaccine candidates.