Administration of tumor necrosis factor (TNF) and gamma interferon (IFN-gamma) to melanoma patients causes selective disruption of the tumor vasculature but the mechanism of this disruption is unknown. Here we report that exposure of human endothelial cells to TNF and IFN-gamma results in a reduced activation of integrin alphaVbeta3, an adhesion receptor that plays a key role in tumor angiogenesis, leading to a decreased alphaVbeta3-dependent endothelial cell adhesion and survival. Detachment and apoptosis of angiogenic endothelial cells was demonstrated in vivo in melanoma metastases of patients treated with TNF and IFN-gamma. These results implicate integrin alphaVbeta3 in the anti-vascular activity of TNF and IFN-gamma and demonstrate a new mechanism by which cytokines control cell adhesion.