1,3-dichloro-5-[(1E)-2-(4-methoxyphenyl)ethenyl]-benzene is a potent and selective antagonist of the aryl hydrocarbon (AH)receptor, which is known to modulate cytochrome P450. 1,3-dichloro-5-[(1E)-2-(4-methoxyphenyl)ethenyl]-benzene is inactive as an estrogen receptor ligand even at 100 M.