Abstract Thalidomide, when administered orally, is an inhibitor of angiogenesis in the basic fibroblast growth factor (bFGF)-induced rabbit cornea micropocket assay. We now show in the mouse that thalidomide given intraperitoneally but not orally significantly inhibits bFGF-induced and vascular endothelial growth factor (VEGF)-induced corneal neovascularization. We further demonstrate that this inhibition is independent from thalidomide's ability to suppress tumor necrosis factor-alpha (TNF-alpha) production. Experiments examining thalidomide's enantiomers reveal that the S(-)-enantiomer has the strongest antiangiogenic activity in VEGF-induced and bFGF-induced corneal neovascularization. Structure activity studies suggest that thalidomide's anti-angiogenic activity is related to the open ring metabolites resulting from hydrolysis. Together these data support a correlation between thalidomide's antiangiogenic and teratogenic activities.