3,4,5,6-Tetrachlorofluorescein is a reactive and monomeric dye that is used in analytical chemistry as a diagnostic agent. It reacts with proteins or peptides to form fluorescent complexes. 3,4,5,6-Tetrachlorofluorescein has been shown to bind to erythrocyte membrane proteins and is excreted in urine. This dye can be used for the detection of protease activity in human serum. 3,4,5,6-Tetrachlorofluorescein has also been used as an innovative pharmaceutical preparation for the treatment of chronic venous ulcers.