Proliferative Diabetic Retinopathy (PDR) is the number one cause of blindness in adults aged 20-65. More effective treatments could help save the vision of millions of people. Extensive research has been focused on the role of growth factors in the development of diabetic retinopathy, which occurs when there is unregulated angiogenesis in the retina. Hepatocyte Growth Factor (HGF), acting through its receptor c-Met, is an important mediator of angiogenesis in multiple other model systems, including tumor angiogenesis and wound healing. In addition, it has been shown to be elevated in the vitreous and epiretinal membranes of diabetics. In this study, we examined the role of Hepatocyte Growth Factor in mediating retinal angiogenesis, using a mouse model of oxygen induced retinopathy (OIR), and Bovine Retinal Microvascular Endothelial Cells (BRMVECs). In addition, we examined the basic retinal phenotype of a transgenic, HGF-overexpressing mouse. We hypothesized that HGF mediates murine retinal angiogenesis through its effects on Matrix Metalloproteinase (MMP) and Urokinase expression. To address this, we examined HGF and c-Met expression in the murine retina, and we analyzed their expression and activity during periods of OIR-induced retinal angiogenesis. In addition, we examined the ability of recombinant HGF (rHGF) to mediate protease expression and invasion in vitro. Finally, we examined the effects of blocking c-Met activation during OIR-induced retinal angiogenesis. Our results indicate that the HGF/c-Met pathway is an important mediator of retinal angiogenesis. Real Time RT-PCR data indicate both genes are upregulated during periods of OIR-induced angiogenesis and the ratio of active c-Met to total c-Met is significantly elevated. Immunohistochemistry and in situ hybridization localizes c-Met expression to capillaries and HGF expression to the ganglion cell layer. Additionally, rHGF induces potent increases in urokinase activity and invasion of BRMVECs in a Matrigel invasion assay. By blocking urokinase association with the urokinase receptor (UPAR), HGF-induced invasion of BRMVECs (Bovine Microvascular Endothelial Cells) is inhibited, indicating that HGF mediates invasion in part through its effects of urokinase activity. Additionally, retinal angiogenesis is dramatically decreased in the OIR model, in which HGF binding to c-Met is blocked. Further, HGF had very little effect on MMP protein expression and activation in both Muller and BRMVECs, and HGF had no effect on urokinase activation in Muller cells. Our findings indicate that the HGF/c-Met pathway mediates retinal angiogenesis by upregulating urokinase activity and inducing an invasive phenotype in retinal microvascular endothelial cells. Our data suggest that blocking the HGF c-Met pathway may inhibit angiogenesis in diabetic retinopathy.