Permanent threshold shifts obtained from 242 chinchillas that were exposed to various impulse noise paradigms have been related to the energy spectra of the impulses. The impulses were generated by three different shock tubes that produced impulse noise spectra whose A-weighted energies showed peaks at 0.25, 1, and 2 kHz. The results show that there is an increasing susceptibility to NIPTS as the audiometric test frequency increases from 0.5 to 16 kHz. This increase in susceptibility to NIPTS is further accentuated by approximately 5 to 10 dB for impulses whose spectra peak at 2 kHz.