Endothelial wound repair was studied in 85 organ-cultured human corneas classed in Groups I--IV by means of a combined silver stain, nuclear stain, and autoradiography after denuding the endothelium from a circular area in the center of the cornea. Endothelial migration into the defect occurred first, but by 48 hours (before the wound was completely covered), incorporation of tritiated thymidine showed synthesis of DNA had occurred. Cell division, shown by the presence of mitotic figures, was greatest at 72 hours. In Group V, the endothelial wound repair was studied in vivo in two patients (a 65-year-old and a 67-year-old). The wound was created by a central transcorneal freeze. After removing the cornea from the enucleated eye, the wound was exposed for one hour to tritiated thymidine at 37 C in vitro. The results of Group V were similar to those of Groups I--IV. Both migration and proliferation were found.