We investigated the distribution of the glutamate receptor subunits, alpha-amino-3-hydroxy-5-methyl-4 isoazolepropionic acid (AMPA) GluR2 and GluR2/R3, and N-methyl-D-aspartate (NMDA) NR1, and the timing of their appearance during early development of the mouse vestibular and spiral ganglia. NMDA NR1 was the first to be expressed, in the statoacoustic ganglion neurons on E11. GluR2/R3 immunoreactivity was detected in these neurons on E12. This signal probably corresponded exclusively to GluR3, as no signal was obtained for GluR2 alone at this stage. The appearance of these proteins began much earlier than previously reported. GluR2 staining was observed later, on E14 in the vestibular neurons and on E17 in the spiral neurons. The sequence in which these three glutamate receptors appeared suggested possible differences in their roles in the establishment of neuronal circuitry in the inner ear sensory epithelia. The production of NR1 and GluR2/R3 began during the early period of neuron growth and fasciculation. GluR2 appeared later and its expression paralleled synaptogenesis in the vestibular sensory epithelia and in the organ of Corti.