Seven beagles were inoculated experimentally with a Swedish canine Ehrlichia species isolate to study its pathogenicity. With respect to the 16S rRNA gene sequence, the isolate was identical to the human granulocytic ehrlichiosis (HGE) agent and closely related to both Ehrlichia equi and E phagocytophila. After an incubation period of four to 11 days, the most prominent clinical signs were high fever for two to five days and depression. All the dogs developed profound thrombocytopenia, moderate leukopenia and a strong serological antibody response. Ehrlichial inclusions were detected in blood neutrophils from four to 14 days after inoculation for four to eight days. Ehrlichial DNA could be detected by polymerase chain reaction during the parasitaemic stage and a few days before and after microscopic inclusions were visible. Postmortem, the dogs showed reactive splenic hyperplasia and non-specific mononuclear reactive hepatitis.