In former studies we showed that risk factors induce an acceleration of the proliferation of the arterial wall cells. Furthermore we examined the influence of acetylsalicylic acid (ASA) upon the proliferation of arterial wall cells of normal animals and of animals which had been damaged by risk factors. We received the following results:1. ASA given to the cell culture inhibits the proliferation of aortic smooth muscle cells (ASMC), endothelial cells and adventitial cells of minipigs,2. ASA given to the culture of ASMC of rats whi ch had been damaged by arterial hypertension, by staphylolysine or by atherogenic diet reduces their increased proliferation rate nearLy to normaL.3. ASA-treatment of rats which had been damaged by injection of staphylolysine reduces the increased proliferation rate of ASMC of these rats nearly to normal.4. It is remarkab le that the induced activation (by risk factors) and the induced inhi - bition (by ASA) of the cell growth persisted in the subcultures.This behaviour is explained by the assumption that the arterial wall has different cell clones, characterized by different proliferation rates: the faster proliferating clones’ are activated by risk factors and the slowlier proliferating clones by ASA. These resuLts are relevant in prevention and therapy of arteriosclerosis.