The β-galactosidase substrate X-Gal (5-bromo-4-chloro-3-indolyl-β-D-galactopyranoside) is a chromogenic stain for β-gal activity, and is commonly used to distinguish between recombinants and nonrecombinants by lacZ α-complementation with appropriate vectors and hosts X-Gal Solution is provided as a convenient 40mg/mL concentrate in DMSO, ready for dilution into culture medium or appropriate buffers