The vasculitides are characterised by vascular inflammation. Endothelial injury is central to the pathogenesis of vasculitis . As a result of the immune – inflammatory necrotic changes in the walls of vessels in the patients with hemorrhagic vasculitis endothelial dysfunction of arterioles and capillaries occurs, contributing to violations of blood rheological properties and microcirculation. Vasculitis can cause abnormal findings an blood counts. Anemia is a typical finding in patients with active vasculitis . A slightly elevated white blood cell count may also occur. Elevated inflammatory markers (erythrocyte sedimentation rate and C – reactive protein ) are also frequently identified in patients with active vasculitis . These processes depend on the age of patients. This thesis focuses in particular on circulating endothelial cells , growth factors involved in vasculogenesis and endothelial progenitor cells.