• Cartilage has been reported to contain a factor that inhibits tumor neovascularization. Rabbit vitreous, another avascular tissue, has also been shown recently to have an inhibitory effect on tumor neovascularization. This report describes our results on the effects of bovine and human vitreous on tumor neovascularization with use of a rabbit cornea model. Inhibition of neovascularization was observed with both bovine and human vitreous in the form of reduced new blood vessel growth over and around the vitreous pellet and subsequent delayed exophytic tumor growth. Stimulation of neovascularization by bovine and human vitreous was also observed as an early, short-lived response.