Corticosteroids have inhibitory effects on corneal endothelial wound healing in organ-culture conditions. Low concentrations of methylprednisolone added to the culture medium inhibited the healing attempt and induced intracellular degenerative vacuoles and diffuse cell disintegration. Higher concentrations were highly toxic to the cell morphology and physiology and caused pronounced endothelial cell damage. These observations are compared with the normal healing of endothelial wounds in organ-culture conditions. Cell proliferation and amitotic and mitotic cell divisions repaired the endothelial layer in normal corneas.