Phlebotonic drugs are very often old drugs which improve symptoms in chronic venous insufficiency but their precise mechanism remains unclear. One reason for this lack of information is our poor understanding of the aetiology of the varicose vein. One hypothesis which is being more and more substantiated is that the origin of the disease lies in the activation of the endothelium during blood stasis, leading to a cascade of reactions which, in the long term, alter the structure of the vein wall. In this work, we tested aescine (Reparil i.v. form), a phlebotonic drug, in an in vitro model which mimics this situation, i.e. human endothelial cells exposed to hypoxic conditions. Aescine was shown to inhibit 2 important steps of the activation of endothelial cells incubated 120 min under hypoxia the decrease in ATP content, which is the starting point of the activation cascade, and the increase in the activity of phospholipase A2, an enzyme responsible for the release of precursors of inflammatory mediators. Hypoxia-activated endothelial cells also increase their adhesiveness for neutrophils. This process could also be prevented in a dose-dependent manner if endothelial cells were incubated in the presence of aescine. This inhibition was confirmed by morphological observations in scanning electron microscopy. All 3 effects were already evidenced at 100 ng/ml and were maximal at 750 ng/ml. These effects obtained at very low concentrations probably represent one of the main molecular and cellular mechanisms that underlie, among others, protection of the vessel wall. Objective criteria for our understanding of the preventive action of this phlebotonic drug are, thus, provided.