Systemic vasculitides are a heterogeneous group of disorders with inflammation of blood vessels as their common pathogenetic hallmark. They often pose difficulties with regard to diagnosis and monitoring of disease activity, both at the initial presentation and during follow-up. Novel markers of disease activity are therefore eagerly awaited. Circulating endothelial cells have recently emerged as one such marker and we have demonstrated their clinical use in ANCA-associated small-vessel vasculitis. Not only entire cells but also endothelial microparticles can be detected in vasculitis although their use is not established to date. Repair of endothelial damage is believed to occur via endothelial progenitor cells and their precise role in vasculitis is also unclear at present. Circulating endothelial cells may complement, rather than replace, conventional markers of disease activity. The ultimate aim of our studies may thus be a panel of various laboratory markers for systemic vasculitis.