The corneal endothelium was examined in ten patients suffering from ocular hypertension before, during and after four months of topical levobunolol treatment. The untreated fellow eye served as a control. The number of endothelial cells, determined with a McIntyre eyepiece and an Eisner's contact lens, was not affected by levobunolol therapy. In addition, the morphology of the cell did not appear to be affected by the drug.