The idea that endothelin ETA and ETB receptors may form homodimers and heterodimers has gained increasing interest in recent years. The existence of such interactions between endothelin receptors has the potential to explain some puzzling results from receptor binding and functional studies. Zeng and colleagues take ETB receptor heterodimerization beyond the ETA receptor, reporting renal endothelin ETB-dopamine D(3) receptor interactions at the cellular level that appear to have functional consequences in vivo.