Pigment epithelium cells autotransplanted into the vitreous cavity of owl monkey eyes, proliferated and metaplased. The metaplastic cells looked like pigmented macrophages, membrane forming fibrocyte-like cells, and frank epithelium cells. This in vivo experiment demonstrated that the vitreous cavity is an adequate culture medium for cells deriving from the pigment epithelium and that pigment epithelium cells could be the source of intraocular proliferation seen in massive periretinal proliferation.