FTY720, a potent immunomodulator, becomes phosphorylated in vivo (FTY-P) and interacts with sphingosine-1-phosphate (S1P) receptors. Recent studies showed that FTY-P affects vascular endothelial growth factor (VEGF)-induced vascular permeability, an important aspect of angiogenesis. We show here that FTY720 has antiangiogenic activity, potently abrogating VEGF- and S1P-induced angiogenesis in vivo in growth factor implant and corneal models. FTY720 administration tended to inhibit primary and significantly inhibited metastatic tumor growth in a mouse model of melanoma growth. In combination with a VEGFR tyrosine kinase inhibitor PTK787/ZK222584, FTY720 showed some additional benefit. FTY720 markedly inhibited tumor-associated angiogenesis, and this was accompanied by decreased tumor cell proliferation and increased apoptosis. In transfected HEK293 cells, FTY-P internalized S1P1 receptors, inhibited their recycling to the cell surface, and desensitized S1P receptor function. Both FTY720 and FTY-P apparently failed to impede VEGF-produced increases in mitogen-activated protein kinase activity in human umbilical vascular endothelial cells (HUVEC), and unlike its activity in causing S1PR internalization, FTY-P did not result in a decrease of surface VEGFR2 levels in HUVEC cells. Pretreatment with FTY720 or FTY-P prevented S1P-induced Ca2+ mobilization and migration in vascular endothelial cells. These data show that functional antagonism of vascular S1P receptors by FTY720 potently inhibits angiogenesis; therefore, this may provide a novel therapeutic approach for pathologic conditions with dysregulated angiogenesis.