Our new surgical treatment for corneal endothelial dysfunction involves replacing damaged the corneal endothelium with healthy corneal endothelial cells cultivated and multiplied in vitro. Monkey corneal endothelial cells (MCECs) were cultivated on collagen type- I carriers for four weeks. The corneal endothelium of the monkeys was mechanically scraped, and the cultivated MCEC sheet was inserted into the anterior chamber and fixed to the Descemet's membrane with air. As controls, a collagen sheet without MCECs was transplanted into one eye, and a suspension of cultivated MCECs was injected into the anterior chamber in another eye. In the early postoperative period MCEC sheets were attached to Descemet's membrane and corneal clarity recovered. This was accompanied by a decrease in corneal thickness. Fluorescein DiI labeled donor corneal endothelial cells were detected on the host cornea on postoperative day7. After transplantation, the MCEC-transplanted corneas remained clear for up to 4 years, and hexagonal cells of a density more than 1,500-2,000 cells/mm2 were observed by in vivo specular microscopy. Control eyes showed irreversible bullous keratopathy. We established a model of cultivated corneal endothelial transplantation for corneal endothelial dysfunction in primates whose corneal endothelial cells have less proliferative capacity in vivo. Our results suggest that this is a useful model for long-term observation in advance of future clinical application of cultivated corneal endothelial transplantation.