Glutamate is thought to be a major neurotransmitter between hair cells and afferent dendrites in the inner ear. However, excessive glutamate is known to be excitotoxic, and may be involved in ischemic neuronal damage in the central nervous system. The glutamate concentration in the perilymph has been reported to increase during ischemia, but the source of glutamate is still unclear. In the present study, we have used post-embedding immunogold cytochemistry to analyse changes in the cellular distribution of glutamate in the guinea pig organ of Corti during ischemia. The areal gold particle densities in the inner hair cells of the ischemic side were lower than those of the control side, indicating that glutamate may be released from the hair cells during ischemia. Adjacent supporting cells (border cells) also showed a decrease in particle density, suggesting that they constitute an additional source of glutamate.