Cochlear microphonics (CM) and masked and unmasked VIIIth nerve action potentials (AP) were measured in rats at ages of one, six, 12, 18 and 24 months in order to explore an animal model for presbycusis. These rats were raised in quiet surroundings and were given no antibiotics. Mean CM 1 microvolt sensitivity levels showed a 7 db augmentation from one month to one year followed by a 13 db decline from one to two years of age. Similarly, unmasked AP amplitudes increased from one to 12 months, then declined through 18 to 24 months. Masked AP amplitudes demonstrated a similar growth and decline with age, showing the greatest losses in those AP components originating from the high frequency regions of the basilar membrane.