Many systemic and eye-specific genetic disorders are accompanied by retinal degenerations that lead to blindness. In some of these diseases retinal degeneration occurs early in life and is quite rapid, whereas in other disorders, retinal degeneration starts later and progresses very slowly. At present, no therapies are available to patients for preventing or reversing the retinal degeneration that occurs in these diseases. Implantation of neural progenitor cells into the eye may be a means by which to retard or even reverse degeneration of the retina. To evaluate the potential of neural precursor cell implantation for treating retinal degenerative disorders, neuralized mouse embryonic stem cells from green fluorescent protein (GFP) transgenic mice were administered intravitreally to normal mice, mice with early retinal degeneration, and mice with slowly progressing retinal degeneration. In normal mice, the donor cells remained in the vitreous cavity and did not associate with the host retina. In mice with early retinal degeneration, implantation of the neural precursors was performed after the degeneration was almost complete. In these animals, the donor cells primarily associated closely with the inner surface of the retina, although a small fraction of donor cells did integrate into the host retina. Donor cells implanted in mice with slowly progressing retinal degeneration also associated with the inner retinal surface, but many more of the cells integrated into the retina. These findings indicate the importance of host tissue-donor cell interactions in determining the fate of implanted neural precursor cells. These interactions will be a major consideration when devising strategies for using cell implantation therapies for neurodegenerative disorders.