Human neonatal corneal endothelial cells were successfully maintained in tissue culture, morphologically resembling adult corneal endothelium. Eyebank donor corneas were obtained, denuded of their native endothelium and seeded with a suspension of the cultivated neonatal endothelial cells. After 48 hours, the eye-bank tissue was then transplanted into the eyes of Rhesus monkeys. Over a five month period, five of eight transplants cleared, with a mean central corneal thickness of 0.480 mm and endothelial cell densities ranging from 560 to 1650 cells/mm2. All control eyes without donor endothelium remained cloudy. In the experimental group three eyes initially thinned but subsequently became edematous. Further studies are needed to improve the seeding procedure and to assess the long-term viability of transplanted endothelium.