The in vivo transplantation of cultured bovine corneal endothelial cells has been attempted in the cat. Cat corneas denuded of their endothelium were coated with bovine corneal endothelial cells previously maintained in tissue culture. When grafted back into cat recipients, the corneal buttons remained clear with no edema. Alizarin red staining of the endothelial side of the corneal transplant demonstrated that the coated bovine corneal endothelial cells reorganized themselves into a highly organized cell monolayer within eight days in vivo. In contrast, corneas denuded of their endothelium became opaque and edematous within seven days and remained so thereafter. These results demonstrate that cultured corneal endothelial cells remain functional in vitro and can replace a damaged or nonfunctional endothelium i