We tested the antibiotic susceptibilities of eight strains of Anaplasma phagocytophilum (the agent of human granulocytic ehrlichiosis) collected in various geographic areas of the United States, including Minnesota, Wisconsin, California, and New York. The results are homogeneous and show that doxycycline, rifampin, and levofloxacin are the most active antibiotics against these strains in vitro.