Data are presented from 14 animals: 8 acoustically traumatized animals (with survival times greater than one year) and 6 unexposed animals (born and raised in a low-noise environment [Liberman, J. Acoust. Soc. Am. 61, S27(A) (1977)]). Electrophysiological data include threshold tuning curves and spontaneous discharge rates from several hundred single units in each case. Epon-embedded surface preparations of the cochleas were examined with the light microscope. Most of the cochleas showed minimal hair cell losses. Histological analysis also included an evaluation of hair cell condition performed by observers without knowledge of the physiological data. inner and outer hair cells were rated on the appearance of their stereocilia, cytoplasmic and nuclear outlines, and as to the quantity of subapical lysosomes. The histological parameters were correlated with the electrophysiological data for the appropriate region of characteristic frequency (according to a previously developed length-frequency map for the cat cochlea). Most interesting was the correlation between magnitude of threshold shift at CF and abnormalities of either inner or outer hair cell stereocilia. [Work supported by NIH.]