5-Bromo-4-chloro-3-indolyl ?-D-glucuronide (BCIG) is an chromogenic enzyme substrate used to detect the presence of glucuronidase enzyme activity. The reaction occurs when BCIG reacts with the enzyme beta-glucuronidase yielding an intense blue color. It is used in a variety of biochemical and biomedical applications, such as the detection of pathogenic bacteria, the diagnosis of genetic disorders, and the isolation of recombinant proteins.