Objective: To observe the effect of noise on the concentration of amino acids in perilymph of the cochlea. Methods: Guinea pigs were either exposed to white noise at 115 dB SPL for 2 h or maintained in silence (40 dB SPL). Perilymph was collected from the cochlea of the both groups. Free amino acids were determined by high-performance liquid chromatography with fluorescence detection. Results: Fourteen kinds of amino acids were detected in the perilymph of the cochlea from the silence group animals. The composition and concentration of these amino acids were similar to those in the guinea pig's cerebrospinal fluid. The concentration of glutamic acid in the cochlea of the noise group was significantly higher than that of the silence group (P<0.01). The average concentration of glutamic acid in the silence group was (6.6±0.2) μmol/L while in the noise group, it was (10.3±1.1) μmol/L. The latter was 55%higher than the former. Conclusion: The glutamic acid in the perilymph of the cochlea can be significantly elevated after exposure to noise. It is inferred that this elevation is caused by over-release of glutamate from hair cells and by reversal of the glutamate transporter.