The authors report the successful in vitro growth of human corneal endothelium derived from 12 of 31 corneal-scleral rims obtained following corneal transplantation. The average age of donors whose endothelium grew was 17.6 +/- 3.2 years. The average interval between death and culturing was 51.5 +/- 10.1 hr. The cells migrated from the explants within 3-7 days and were characterized by a flattened, polygonal shape with a centrally located nucleus. Cell growth exhibited a doubling time of 72-96 hr in the second and third tissue culture passages. A reduced growth rate was observed by cell lines maintained in vitro for over 6 months. Fibroblast growth factor, epidermal growth factor, and endothelial cell growth supplement all exerted a positive influence on cell proliferation. Corneal-scleral rims can be a valuable source of endothelial cells for corneal research.