Pigment epithelium derived factor, originally identified in conditioned medium of cultured human fetal retinal pigment epithelial (RPE) cells, is a neurotrophic protein that induces extensive neuronal differentiation in human Y79 retinoblastoma cells, a neoplastic counterpart of normal retinoblasts. It has been suggested that PEDF is synthesized by RPE cells and secreted into the retina interphotoreceptor matrix where it may influence development/differentiation of the neural retina. PEDF is a