To study vascular endothelium in patients with systemic vasculitis (SV) with non-invasive methods.A total of 65 SV patients entered the trial: 20 patients with Henoch-Schonlein purpura (HSP), 20 patients with thromboangitis obliterans (TO), 10 patients with polyarteritis nodosa (PN), 15 patients with Takayasy's arteritis (TA). The control group consisted of 30 subjects. Endothelium-dependent vasodilation (EDV) was assessed with the ultrasonic technique by D. Celermajer et al., endothelium-independent vasodilation (EIV)--with a nitroglycerin test. The coefficient of sensitivity (CS) of the brachial artery to reactive hyperemia was calculated.In all SV forms EDV was reduced. Three types of response to the tests were registered: normal (24.6%), insufficient (41.6%) and paradoxical (33.8%). Changes in EDV and EIV were revealed: in HSP--a moderate decrease of EDV and EIV; in TA--affection of EDV with frequent paradoxical reactions and noticeable decrease of EIV; in PN--a moderate decrease of EDV and affection of EIV; in TO--affection of EDV and unaffected EIV In SV patients CS was reduced even in patients with normal response to reactive hyperemia. Correlation of EDV with clinical symptoms of SV was found.In SV changes in EDV and EIV as well as CS are caused by endothelial dysfunction. CS serves as an additional criterion of endothelial function impairment in unaffected EDV Correlation of EDV changes with clinical symptoms points to pathogenetic value of endothelial dysfunction in SV.