PXR (also known as orphan nuclear receptor PXR, pregnane X receptor, orphan nuclear receptor PAR1, and steroid and xenobiotic receptor (SXR)) is a member of the nuclear hormone receptor family, NR1 subfamily containing a zinc finger domain. Alternatively spliced variants of this receptor have been reported. This nuclear protein has a molecular weight of 50 kD and is highly expressed in liver, colon, and small intestine. PXR is an orphan receptor whose natural ligand is probably pregnane. PXR binds to the promoter response element in cytochrome p450 gene monooxygenase CYP3A4 and activates expression in response to variety of endobiotics and xenobiotics. PXR is activated by naturally occurring steroids such as pregnenolone and progesterone and can also be activated by dexamethasone and rifampicin. PXR forms a heterodimer with RXR. The Poly6169 antibody recognizes human and mouse PXR and has been shown to be useful for Western blotting.