RETINOID X receptor (RXR) plays a central role in the regulation a of many intracellular receptor signalling pathways(1) and can mediate ligand-dependent transcription, acting as a homodimer or as a heterodimer(1-6). Here we identify an antagonist towards RXR homodimers which also functions as an agonist when RXR is paired as a heterodimer to specific partners, including peroxisome proliferator-activated receptor and retinoic acid receptor. This dimer-selective ligand confers differential interactions on the transcription machinery : the antagonist promotes association with TAF110) (TATA-binding protein (TBP)-associated factor 110) and the co-repressor SMRT(7), but not with TBP, and these properties are distinct from pure RXR agonists. This unique class of RXR ligands will provide a means to control distinct target genes at the level of transcription and allow the development of retinoids with a new pharmacological action.