Pigment epithelium-derived factor (PEDF) is a multipotent neurotrophic factor with potent activity both in the central nervous system and in the retina. To date, PEDF is the most potent angiogenic inhibitor found in the mammalian ocular compartment. Recent studies have shown that decreased ocular levels of PEDF are associated with diabetic retinopathy and other neuroretinal dystrophic diseases. In addition, the neurotropic and anti-angiogenic properties of PEDF suggest this protein is of potential therapeutic value for control of neovascularization associated with tumor growth. To facilitate research on this important member of the serpin protein superfamily, we have developed a sensitive PEDF ELISA using polyclonal antibodies that specifically detect native PEDF protein in human vitreous and other tissues.