Amino acid concentrations were measured in the cochlear nucleus for a group of 20 chinchillas: four each of control and 4, 8, 29, and 85 days after treatment with the ototoxic anti-tumor drug carboplatin (100 mg/kg, i.p.). The treated chinchillas showed various extents of inner hair cell loss, generally more complete at longer survival times, but little loss of outer hair cells. Aspartate concentration in rostral anteroventral cochlear nucleus (AVCN) showed a decline to 28% less than the control value at 29 and 85 days after treatment, whereas glutamate concentration showed little change through 29 days, then dropped by 22% at 85 days after treatment. In caudal posteroventral cochlear nucleus (PVCN), the aspartate concentration decreased by 32% at 29 days, in animals with significant inner hair cell loss, and 48% at 85 days after treatment, while the glutamate concentration showed no decrease through 29 days and 40% decrease at 85 days. The concentration of gamma-aminobutyrate (GABA) was about 18% lower than control in caudal PVCN at all survival times. Significant correlations were found between the proportion of inner hair cells remaining and glutamate and aspartate concentrations in PVCN and AVCN, but not GABA or other amino acids.