Absolute thresholds were determined in the chinchilla using a new behavioral procedure. The animal was reinforced with a 45-mg pellet (Noyes) for depressing and holding a key 1–7 sec and either releasing it during a 2-sec tone presentation or not releasing it during a 2-sec catch trial. Using a tracking procedure, thresholds were determined at 9 to 15 frequencies during each daily 1-hour session. Thresholds are compared to those obtained by conventional shock-avoidance techniques, and the advantages and disadvantages of the procedure are considered. Following threshold determinations, two of the animals were exposed to a 123-dB two-octave band of noise (710–2800 Hz) for 15 minutes. The animals were sacrificed 7 and 28 days post exposure, respectively and their cochleas prepared for examination under the light microscope by the surface preparation technique. The correlation between the amount of hearing loss present and the cochlear pathology is examined, and these results are compared to those obtained by Ward and Duvall [Ann. Otol. 80, 881 (1971)]. [Research supported by NIH research and training grants.]