5-Bromo-4-chloro-3-indoxyl butyrate is a colorimetric substrate used to detect and quantify esterase activity. Upon hydrolysis by esterases, it yields a blue-green dye, allowing the detection and quantification of enzyme activity. It is commonly used in assays for the screening of esterase-producing microorganisms and in research aimed at understanding the role of esterases in various cellular processes.