Breaks or tears in the endothelium and Descemet's membrane (DM) are easily noticed in exact biomicroscopical ophthalmological examination. We present 2 patients with a large unilateral horizontal rupture in Descemet's membrane and abnormal corneal endothelia. In the area of the rupture the endothelial mosaic was highly abnormal, and there was no cell reflex. At the site of the rupture and at the periphery of the cornea of the affected eye the endothelial cell density was distinctly lowered, with pleomorphism and polymegathism. In an eye with a DM rupture and degenerated endothelium, difficulties in contact lens wear seem to be due to the hypoxia caused by soft contact lenses. For such patients, only gas-permeable hard lenses with short wearing times should be recommended. Check-ups should be frequent and meticulous. To ensure that endothelial degeneration is noticed well before corneal damage is clinically evident, the endothelial cells must be counted and changes sought for by specular microscopy.