Human corneal endothelial cells have been grown in mass culture for the first time to our knowledge. Cultures from donors who were under 20 years of age grew well. Cells from older donors were difficult to grow or did not grow at all. Initial outgrowth usually began one week after explantation. After an initial lag phase, mass increased by 15% weekly, and confluency was approached in eight to nine weeks. The lag phase of growth correlated with the age of the donor. A basal lamina was secreted by human corneal endothelial cells in culture. Chromosomal counts demonstrated a modal number of 46. With this technique, sufficient human corneal endothelial cells may be obtained for biochemical investigation.