Ehrlichia spp. are obligate intracellular bacteria with tropism for hematopoieticcells. Monocytic ehrlichioses in dogs and humans are transmitted by ticks and primarily caused by E.canis and E. chaffeensis, respectively. E. canis causes canine monocytic ehrlichioses (CME), a potentiallyfatal disease in dogs that requires rapid and accurate diagnosis in order to initiate appropriate therapyleading to a favorable prognosis. CME is characterized by three stages; 1) acute, 2) subclinical and3) chronic. Dogs infected with E. canis remain infected for their entire lives, even after receivingantibiotic treatment with doxycycline. The prevalence of E. canis is dependent on the distribution ofthe vector, Rhipicephalus sanguineus tick, which occurs mainly in tropical and subtropical regions. Theagent causing canine granulocytic ehrlichiosis (CGE) in Europe has been determined by nucleotide sequencingof the 16S rRNA gene to be similar to both Ehrlichia equi and E. phagocytophila (Anaplasma phagocytophila),and is identical to the agent of human granulocytic ehrlichiosis (HGE). The vector of this pathogen inEurope is the common European tick, Ixodes ricinus and its reservoir - wild and domestic animals. Twodistinct clinical disease syndromes, including chronic, moderate to sever anemia and polyarthritis, areassociated with CGE. In areas infested with vectors of tick-borne agents known to be endemic for Lymedisease, veterinarians may suspect ehrlichiosis in dogs.