Isopropyl-beta-D-thiogalactopyranoside (Dioxan free) is a non-metabolizable allolactose analogue.

Isopropyl β-d-1-thiogalactopyranoside (IPTG) is a molecular biology reagent . It is used to induce protein expression where the gene is under the control of the lac operator. It is also often used in cloning procedures that require induction of β-galactosidase activity.

IPTG functions by binding to the lacI repressor and altering its conformation, which prevents the repression of the β-galactosidase coding gene lacZ.