There is a hypothesis that corneal endothelial cells migrate after penetrating keratoplasty from the areas of higher cell density to the lower cell density areas. In order to confirm this hypothesis, the author performed exchange penetrating keratoplasty in normal albino rabbits using four combinations of sex and age and examined the movement of the endothelium between donors and recipients by observing the density and sex chromatin of the endothelial cells. As a result, there was no significant difference of the rate of decrease of the endothelial cell density of the postoperative grafts between young and old grafts. In the experiment using the sex chromatin of the endothelial cells as a cell marker, it was concluded that the endothelium of the rabbit cornea migrate from the young grafts to the old recipients or from the young recipients to the old grafts. In the control study exchanging rabbit grafts between animals of different sex but the same age the count of the sex chromatin of the endothelium of the grafts and recipients did not change postoperatively. The results confirmed the above hypothesis concerning the migration of the transplanted corneal endothelial cells in the rabbit cornea.