Nine Norwegian Red Cattle, 9-12 months old, were inoculated simultaneously with Ehrlichia (Cytoecetes) phagocytophila and Babesia divergens. Ten cattle of the same breed and age were kept as controls. Clinical evaluation was done on a daily basis and rectal temperatures were recorded every morning for 4 weeks post inoculation. Blood and serum samples were collected regularly during the observation period. Sera were examined for the presence of antibodies to E. phagocytophila and B. divergens by an indirect immunofluorescence antibody test. All infected animals showed two periods of fever that corresponded to the proliferation of B. divergens and E. phagocytophila in the peripheral blood. The simultaneous infection did not induce more severe clinical symptoms than infection with either organism alone. Compared with the control group, there was a 25% decrease in the mean haematocrit. The leukogram showed a biphasic pattern and corresponded to the changes seen in infection with either organism alone. The simultaneous infection did not suppress antibody formation towards E. phagocytophila or B. divergens.