Notch-noise masking was used to measure frequency tuning in a dolphin (Tursiops truncatus) in a simultaneous-masking paradigm in conjunction with auditory brain-stem evoked potential recording. Measurements were made at probe frequencies of 64, 76, 90, and 108 kHz. The data were analyzed by fitting the rounded-exponent model of the auditory filters to the experimental data. The fitting parameter values corresponded to the filter tuning as follows:QER(center frequency divided by equivalent rectangular bandwidths) of 35 to 36.5 andQ10 dBof 18 to 19 at all tested frequencies.