The semiconductor element, germanium (Ge), is essential for the manufacture of modern integrated circuits. Because of its anti-tumor and immunomodulative effects, Ge-containing compounds are also used as health-promoting ingredients in food. However, some histological studies have shown the toxic effects of Ge-containing compounds on various organs, including the central nervous system. Even now, the effect of germanium on auditory system function is not completely clear. To clarify this question, brainstem auditory evoked potentials (BAEPs) were applied to examine the effect of germanium dioxide (GeO(2)) on the ascending auditory pathway. Since the voltage-gated sodium channel is important to neuron activation and nerve conduction, the effect of GeO(2) on voltage-gated sodium channels was also examined. The result revealed GeO(2) elevated the BAEPs threshold dose-dependently. GeO(2) also prolonged latencies and interpeak latencies (IPLs) of BAEPs, but the amplitudes of suprathreshold intensities (90dB) did not show any obvious change. In addition, the results of whole cell patch clamp studies indicated GeO(2) reduced inward sodium current. These results suggest the toxic effect of GeO(2) on the conduction of the auditory system, and that inhibitory effect of GeO(2) on the voltage-gated sodium channels might play a role in GeO(2)-induced abnormal hearing loss.