Four kangaroo rats were conditioned by shock avoidance and their auditory thresholds determined from 125 through 8,000 Hz. The middle ears were reduced and thresholds re-determined. Normal mean thresholds range from about 9 dB at 1,000 Hz, to 21 dB at 125 Hz and 19 dB at 8,000 Hz. At 1,000 Hz and below, volume reduction causes a loss of 10 dB or more in sensitivity. The method is described and its difficulties discussed. The importance to kangaroo rats of low- rather than high-frequency sensitivity, and the proposed role of the middle ear cavity, are also discussed.