Primate (baboon) corneal endothelial cells have been grown continuously in vitro for over 40 passages. Endothelial cells migrated from the explants within three to five days. Growth became confluent by 14 to 21 days; the cells in culture were polygonal in shape and formed a compact monolayer. In passages one to four, cells divided with a doubling time of 72 hours; this increased to 96 hours after the 16th passage. Even though the general morphological appearance was unchanged in passages greater than 10, the cells became irregular, exhibiting an enlarged and elongated profile. The addition of epidermal growth factor to the medium resulted in increased cell growth. Cultured cells were successfully transplanted onto Descemet's membrane of de-endothelialized baboon corneas. This study demonstrates that primate corneal endothelial cells can be grown continuously in tissue culture and subsequently transplanted in vitro.