2-Naphthyl 2,3,4,6-tetra-O-acetyl-b-D-glucopyranoside (NAG tetra acetate) is a chromogenic enzyme substrate commonly used in the detection of beta-galactosidase activity. Upon hydrolysis by the enzyme, it produces a yellow product that can be detected by spectrophotometry or visually. It is frequently used in bacterial assays to monitor gene expression or as a tool for screening potential inhibitors of the enzyme.