Anaplasma ovis was experimentally transmitted from domestic sheep to elk (Cervus elaphus) and hack to splenectomized sheep. No rickettsemias were detected but serum from three of seven experimentally inoculated elk developed Anaplasma spp.-reactive antibody as measured by indirect immunofluorescence (IIF) or by the rapid card agglutination and complement fixation assays. Three elk were experimentally infected with A. marginale. The rickettsiae were detected in blood of these elk and caused disease in a splenectomized domestic bovine calf after subinoculation of blood from the elk. All three elk had positive titers with IIF. No clinical signs of illness were noted in any elk inoculated with either Anaplasma species.