Hypo and hypercholesterolemic rats strains were selected (Lyon) and compared to a normocholesterolemic one issued from the same race (Sprague-Dawley). The arterial tissue of these three strains at three ages (10-19-25 months) and their reactivity to an hyperlipidic diet (2 and 6 month duration) were studied using histological and histochemical technics. There were neither histological nor histochemical differences between the three strains whatever the ages. Therefore, at the present stage of selection, the genetic differences have not changed the arterial metabolism or its evolution during ageing. However the arterial reactivity of hypo and hypercholesterolemic strains towards an hyperlipidic diet was different: indeed both strains developed hypercholesterolemia, liver steatosis and diffuse intimal lipoidosis, but on the other hand the hypercholesterolemic rat alone demonstrated arterial cell proliferation. These data suggest that a same genetic trait can give rise to both a spontaneous hypercholesterolemia and an arterial hyperactivity against a superimposed hyperlipemia.