The invention provides peptide compositions and mixtures useful for the detection of antibodies that bind to Ehrlichia antigens. The peptide compositions and mixtures comprise polypeptide sequences based on an immunogenic fragment of the Ehrlichia Outer Membrane Protein 1 (OMP-1) protein. The invention also provides devices, methods, and kits comprising such peptide compositions and mixtures useful for the detection of antibodies that bind to Ehrlichia antigens and the diagnosis of monocytic and/or granulocytic ehrlichiosis.