BCIP Red (5-Bromo-6-chloro-3-indoxyl phosphate, <i>p</i>-toluidine salt ) is a derivative of BCIP chromogenic phosphatase substrate. While BCIP yields a blue precipitating product, BCIP Red produces a red (&lambda;_max 565 nm) colored precipitate. This kit contains 100 mg each of BCIP Red and the oxidant NBT (Nitro blue tetrazolium), which facilitates precipitation of the substrate.