The expression of mRNAs encoding five putative non-NMDA glutamate receptors was investigated using in situ hybridization with radiolabeled riboprobes. Hybridization was observed in spiral ganglion neurons with probes complementary to mRNA products of the glutamate receptor genes GluR2 and GluR3. No specific hybridization was observed with probes for GluR1, GluR4 or GluR5. The results support the hypothesis that glutamate is the transmitter between cochlear inner hair cells and spiral ganglion neurons, and that it acts via non-NMDA glutamate receptors.