An abbreviation for isopropyl-ß-D-thiogalactoside. A gratuitous inducer of the lac operon. That is, it can induce expression of the lac operon but it is not a substrate for the lac gene products.

IPTG is a common abbreviation for Isopropyl β-D-1-thiogalactopyranoside, a molecular biology reagent. It has a molecular weight of 238.3.