The peripheral membrane protein gephyrin is essential for the postsynaptic localization of inhibitory glycine receptors (GlyRs). Binding of gephyrin to the GlyR β subunit is mediated by a sequence motif located in the intracellular loop region connecting transmembrane segments 3 and 4. Here, insertion of this binding motif is shown to alter the subcellular distribution of an excitatory neurotransmitter receptor in transfected mammalian cells. Upon coexpression with gephyrin, a mutant N-methyl-d-aspartate (NMDA) receptor containing NMDA receptor 1 (NR1) subunits which harboured a gephyrin-binding motif within its cytoplasmic tail region, was targeted to intracellular gephyrin-rich domains, as previously observed for the GlyR β subunit. Our data indicate that a gephyrin-binding motif located in a cytoplasmic domain of an integral membrane protein suffices for routing to gephyrin-rich domains.