Interleukin-8 (IL-8) is a chemokine involved in angiogenesis, a process vital to tumor growth. Previously, we showed that endothelial cells derived from human tumor tissue have different functional and phenotypic properties compared with normal endothelial cells. This study analyzes the role of IL-8 in regulating angiogenesis of tumor-associated brain endothelial cells (TuBEC). Results show that TuBECs have a higher baseline migration rate compared with normal brain endothelial cells (BEC). TuBECs are unaffected when stimulated with IL-8 whereas BECs are activated. This lack of response of TuBECs to IL-8 is due to the constitutive production of IL-8. Endogenously produced IL-8 activates TuBECs in an autocrine manner as shown by IL-8 receptor inhibition. Blocking either CXCR1 or CXCR2 partially reduces TuBEC migration, whereas blocking both receptors further reduces migration. Treatment with antibody against vascular endothelial growth factor (VEGF) shows that production of IL-8 by TuBECs is dependent on VEGF. Transforming growth factor-beta1 (TGF-beta1), shown to down-regulate IL-8 production in BECs, does not inhibit IL-8 production in TuBECs. In summary, these studies show that TuBECs constitutively secrete IL-8 and autocrine activation by IL-8 is the result of VEGF stimulation. Furthermore, TuBECs do not respond to the feedback inhibition normally induced by TGF-beta1. These data emphasize the functional uniqueness of TuBECs. Understanding the functions and regulatory processes of tumor-associated endothelial cells is critical for developing appropriate antiangiogenic therapies.