The metabotropic GABAB receptors mediate slow synaptic inhibition and consist of heterodimers of GABAB1 and GABAB2 subunits. The only known molecular diversity of the GABAB receptors arises from the two GABAB1 isoforms, but its functional significance has been unclear. Two studies in this issue of Neuron now demonstrate that GABAB1a and GABAB1b show strategically distinct subcellular localization and physiological action.