Plasmatic levels of endothelial markers [von Willebrand's factor (VWF), fibronectin (FN), and angiotensin converting enzyme (ACE)] were measured in patients at various stages of evolution of HIV1 infection. VWF levels were elevated at all stages, while other markers were significantly altered only for the most advanced stages. These results can be interpreted as indicating an endothelial involvement during HIV infection and VWF being the most sensitive marker. Endothelial markers, mainly VWF, could be used as prognosis marker of the infection. Capillary density was measured in the dermis of uninvolved skin showing a significant angiogenesis associated with the HIV1 infection. These biochemical and histological results however do not indicate whether these changes are directly linked to endothelial infection by the virus or to an indirect effect. The endothelial cell being an immunocompetent cell what is its involvement in the genesis of the immuno deficiency syndrome?