The corneal endothelium plays a major part in corneal deturgence and hydratation by functioning as a barrier and a pump. Fluorophotometry enables assessment of this barrier function because of endothelial permeability to fluorescein. After a description of the technique of fluorophotometry, the authors show its interest in the understanding of endothelial physiopathology: during aging, in compensated or decompensated endothelial dystrophy, during lens and corneal surgery, in irido-corneal endothelial syndrome and in pharmacology.