Olfactory nerve axons terminate in rounded regions of the olfactory bulb, termed glomeruli, where they make excitatory synapses with the dendrites of second-order neurons. Neurotransmission from the olfactory nerve to the postsynaptic targets is negatively regulated by gamma-aminobutyric acid (GABA), and there is evidence that inhibition of sensory input is mediated, at least in part, by GABA(B) receptors. Using an antiserum that recognizes two GABA(B) receptor splice variants (GBR1a and GBR1b), we show here that GABA(B) receptors are located on the axon terminals of the olfactory nerve, where they are concentrated at sites of axodendritic apposition. Taken with previous data, these results indicate that GABA(B) receptors act presynaptically to regulate the release of glutamate from olfactory nerve terminals.