In patients with traumatic brain injury (TBI), hypoperfusion contributes to ongoing and expanding areas of neuronal damage long after the initial trauma has ceased. In order to evaluate whether the antiangiogenic protein endostatin may play a role in this process, we analyzed its spatial distribution in brains of 18 patients with TBI. We observed an increase of endostatin/collagen XVIII(+) macrophages/microglial cells but not astrocytes up to day 14 and a consequent decrease to day 16 post-TBI. In addition, paracellular endostatin/collagen XVIII deposits were detected. In vitro experiments revealed that microglial endostatin release is induced predominantly by hypoxia and, to a lesser extent, by reactive oxygen intermediates. Common NO synthase inhibitor pharmacotherapy with aminoguanidine and L-NAME completely abolished endostatin release from microglial cells, raising hopes of altering endostatin release in vivo.