Babesia canis, a hemosporidia parasitizing the erythrocytes of dogs, probably has been studied as carefully as any of the species of the family BABESIDAE. Since the historical and morphological aspects of this sporozoon have been covered adequately by Schilling and Meyer (1930), Wenyon (1926), Hegner (1938a) and Saunders (1937) they will not be reviewed here. A part of the symptomatology associated with infection by this blood parasite is a marked anemia which, as far as the authors are aware, has not been described in detail. In the present paper an attempt will be made to describe the anemia and the corresponding erythrocyte changes.