Ecologie et rôle pathogène de Dermacentor reticulatus (Fabricius, 1794) (lxodoidea) dans le sud-est de la France. - D. reticulatus, a tick very widespread in south-eastern France down to the latitude of Montelimar, lodging essentially in fresh or medium dry vegetable surroundings, has a marked preference for certain biotopes such as: pastured land, formerly mowed meadows, ’waste land’ in cities, heath, scattered shrubs. Its activity is verno-autumnal, reaching climax in spring. The genesis of suburban and certain rural biotopes appears to be related to the ecological disorders relevant to a human presence which, via animais, exerts itself without distinction within too restricted spaces. This tick is the agent of important animal diseases (piroplasmosis of Babesia caballi and Babesia canis); its effects upon human epidemiology, not yet defined, should be reconsidered in the light of recent data concerning its ecology.