Anaplasma ovis was experimentally transmitted from sheep to pronghorn antelope (Antilocapra americana) and back to sheep. Anaplasma ovis was recovered in splenectomized sheep, from two of three spleen-intact pronghorns following their inoculation with blood from known A. ovis carrier sheep. These two pronghorns exhibited a 0.5% or higher A. ovis parasitemia within 48 days after exposure, and an anaplasmosis-positive serological response 91 days after exposure. Clinical signs of illness were not observed. Blood from the infected pronghorns produced disease in four splenectomized sheep.