Retinal neovascularization is the major cause of untreatable blindness, The role of growth hormone (GH) in ischemia-associated retinal neovascularization was studied in transgenic mice expressing a GH antagonist gene and in normal mice given an inhibitor of GH secretion (MK678), Retinal neovascularization was inhibited in these mice in inverse proportion to serum levels of GH and a downstream effector, insulin-like growth factor-I (IGF-I), Inhibition was reversed with exogenous IGF-I administration, GH inhibition did not diminish hypoxia-stimulated retinal vascular endothelial growth factor (VEGF) or VEGF receptor expression, These data suggest that systemic inhibition of GH or IGF-I, or both, may have therapeutic potential in preventing some forms of retinopathy.