application： 5-Bromo-3-indolyl-β-D-galactopyranoside is an α-galactosidase substrate which is converted to an insoluble indigo-blue chromophore darker than that released by X-GAL. It is ideal for Lac gene detection systems in immunoblotting, immunocytochemical, and histological applications. Also used as chromogenic substrate that is suitable for identification of lac-(+) bacterial colonies.