3,3',5,5'-Tetramethylbenzidine
（重定向自Tetramethylbenzidine）
3,3’,5,5’-Tetramethylbenzidine or TMB is a chromogenic substrate used in staining procedures in immunohistochemistry as well as being a visualising reagent used in enzyme-linked immunosorbent assays (ELISA). TMB is a white crystal powder that forms a pale blue-green liquid in solution with ethyl acetate. TMB is degraded by sunlight and by fluorescent lights.