Compounds and methods for the diagnosis and treatment of Ehrlichia infection, inparticular human granulocytic ehrlichiosis, are disclosed. The compounds provided include polypeptides that contain at least one antigenic portion of an Ehrlichia antigen and DNA sequences encoding such polypeptides. Pharmaceutical compositions and vaccines comprising such polypeptides or DNA sequences are also provided. Diagnostic kits containingsuch polypeptides or DNA sequences and a suitable detection reagent may be used for the detection of Ehrlichia infection in patients and biological samples. Antibodies directed against such polypeptides are also provided.