90 corneas from patients, 40 to 80 years old, who had died from carcinoma of mammary gland, lungs and other organs, and 20 corneas from patients of the same age dying from cardiovascular diseases, were studied. The density of endothelial cells was significantly increased in carcinoma patients (for example, 2939 cells/mm2 versus 2160 in control at the age of 40-60 years) with a simultaneous decrease of the cell surface. There was an increase in the number of cells with a small surface and a decrease in the number of binuclear cells. Mitosis (mainly prophase and telophase) is found in the endothelial cells of cancer patients.