Our purpose was to evaluate the role of specular microscopy in the assessment of donor corneas for transplantation. We conducted retrospective analysis of specular microscopic evaluations of 1,000 consecutive donor corneas processed at Mayo Clinic Eye Bank from 1986 to 1993. Thirty-four of the 1,000 corneas were excluded from transplantation use on the basis of specular microscopic examination. Twenty-four corneas were excluded because of the presence of dark spots on the endothelium that did not clear with time. Large endothelial cells were found in six corneas on inspection, with a mean cell density of 1,160 cell/mm2 (795-1,597 cells/mm2). The remaining four excluded corneas showed evidence of endothelial trauma. Of 966 corneas not excluded, 520 (mean cell density 2,632 cells/mm2, range 1,621-4,590 cells/mm2) were transplanted at the Mayo Clinic, and the rest were distributed for transplantation elsewhere, when possible. Six of the corneas transplanted at the Mayo Clinic (1.2%) failed primarily. There ware no significant differences in the preoperative characteristics of the donor corneas between the donor failures and the clear grafts. Specular microscopic examination excluded 3.4% of donor corneas on the basis of unsatisfactory endothelium. Despite examination of the endothelium, six of 520 transplanted corneas (1.2%) suffered primary graft failure. Morphologic assessment of donor corneal endothelium by specular microscopy probably lessens, but does not eliminate, the risk of primary donor failure.