Dermacentor marginatus is a speê:ies very widely spread in the countries surrounding the Mediterranean, temperate Europe and more continental regions (The Soviet Union .. . ). Many observations nave been made in the SouthEast of France and lead to precisions concerning its distribution in the French Alps and the pre-alpine countries. The study of the relations between. the species and vegetation show off a particular a ffinity for the pubescent oak-series (and particularly submediterranean series of the pubescent oak). Dermacentor marginatus is also weil representated in mcdiferranean series on the one hand, and in mesophilous series of continental Europe on the other hand . The biotopes are particularly numerous in meadows that were grazed on at the beginning of the colonization by the woods, in the dwarf-shrubs heaths in which Papilionaceae (Genista cinerea, Cytisus scoparius, Spartiwn junceum ... ) predominate and along the hedges. The species may be collectcd also in the halophytic grouping and salt meaclows of Camargue. Dermacentor marginatus could be playing a part in the epidemiology of many diseases.