The retinal pigment epithelial cells (RPEs) are a monolayer of cells underlying and supporting the neural retina.Here we show that a subpopulation of adult human RPEs can be activated in vitro to proliferate extensively, and can differentiate into neuronal cells with expression of tyrosine hydroxylase (TH).Since RPEs naturally generate levodopa, the precursor for dopamine, such TH+ human RPE-derived neuronal cells are able to produce dopamine, and can be used for treating Parkinson's disorders.